ACVPM Epidemiology and Biostats

Name at least three things that you would place in the epidemiological triad under the "host" category for Q fever

Cattle, sheep, goats = primary reservoir Most animals are subclinical Clinical disease in animals is either abortion (storms), stillbirth, endometritis, mastitis, or infertility

US Preventive Services Task Force (USPSTF) makes suggestions for clinical services/tests to be provided in practice using various grades (A through I). What are these grades based on?

Certainty of net benefit. Grade A is the highest and thus would suggest to offer or provide a service rated Grade A (as well as B).

To prove causation, what must be true regarding biological gradient?

Changes in exposure relates to changes in disease risk - an association is more likely to be causal if the frequency of disease varies directly with the amount of exposure

If you have several samples of proportions you wanted to compare, what tests could you run (3)?

Chi square test Logistic regression Poisson regression

Hypothesis testing for a single population variance follows what distribution?

Chi squared

What test compares observed number to expected number of observations?

Chi squared

If you want to make inference about the relationship between two categorical variables, what tests could you run (3)?

Chi squared test Logistic regression Poisson regression

What are the 3 types of statistical tests that are used to compare counts or proportions within nominal data?

Chi squared test (2 or more independent groups) Fisher's exact test (2 or more independent groups but at least 20% or greater of the expected frequencies is less than 5) McNemar test (one group)

The _______ test tests whether the observed differences in proportions between study groups are statsitically significant

Chi-square test

If you have two samples of proportions, what test would you run?

Chi-square test or two sample z-test

What is an example of an experimental study design?

Clinical Trial

After meta analysis, the next strongest study type is the?

Clinical trial

A ____________ is considered to be cases group in time or space, but may not represent a real increase over the expected number in a given time period

Clust

A ______________ study initially classifies subjects based on whether or not they have a risk factor, then follows them over time to see if they do or do not develop disease.

Cohort

A _________________ study typically examines multiple health effects of an exposure. Subjects are defined according to their exposure levels and followed for disease occurence

Cohort

In a ______________ study there is known exposure status of individuals, and you compare outcome occurrence between groups

Cohort

What are the two primary study designs used in outbreak investigations?

Cohort Studies Case-control studies

Cohort studies are best when the exposure is (common/rare) and the disease is (frequent/infrequent) among the exposed

Cohort studies are best when the exposure is rare and the disease is frequent among the exposed

What method of carcass disposal is quick, cost efficient, has a high temperature destruction of the disease agent, is an on farm alternative to burial, and requires cover?

Composting

_______________ __________________ report the level of certainty in calculated point estimates

Confidence intervals

In an outbreak investigation, an animal with a positive test result from definitive diagnostic, such as testing from the NVSL lab, would be considered a __________ case

Confirmed positive case

_____________ is the distortion of an exposure -disease association by the effect of some third factor

Confounding

What are the clinical signs in mares with Contagious Equine Metritis?

Copious vaginal discharge

What type of regression is performed for survival analysis (time-to-event)

Cox proportional hazard (PH) model

Name at least three things that you would place in the epidemiological triad under the "agent" category for Q fever

Coxiella burnetti intracellular zoonotic agent shed in birth products, feces, urine, milk semen Transmitted by contact, aerosol, oral, tick bite Highly infectious (low human infectious dose)

What study design has patients randomized to groups, observed, then switch groups and obseved?

Cross over study design Note: each patient serves as his or her own control, and this can reduce ethical concerns of no treatment

In a _____________ study, a snapshot of exposure an outcome in population at a specific time point is given

Cross-sectional or prevalence study

In a ____________ study, you will take a representative sample from a population and find out which have the disease and which do not. Then you will ask, what is different about these two groups, and is that difference associated with the outcome?

Cross-sectional study

US Preventive Services Task Force (USPSTF) makes suggestions for clinical services/tests to be provided in practice using various grades (A through I). What does a grade I mean?

Current evidence is insufficient to make a recommendation, therefore, balance of benefits and harms cannot be determined

US Preventive Services Task Force (USPSTF) makes suggestions for clinical services/tests to be provided in practice using various grades (A through I). Which grade suggests to discourage the use of a service?

D

What are four ways to reduce the R0?

DECREASE Transmission constant (measure of susceptibility and contact rate between hosts) DECREASE Number of susceptibles INCREASE Recovery rate INCREASE Host death rate

_______________ epidemiology uses data to characterize outbreaks by farm/animal, place and time

Descriptive

___________ bias is persons followed more closely by health care providers because of some exposure are more likely to be diagnosed as a case

Detection (aka surveillance or diagnostic) bias

When you are comparing the observed versus the expected number of cases, what step are you doing in an outbreak investigation?

Determining the existence of an outbreak (># than expected cases)

What is the test run to determine if a logistical regression model is a good fit for the data?

Deviance Smaller deviance = better fit; if testing, you would get a high p value that leads you to NOT reject the null, which suggests the two are similar, so it WOULD be a good fit in this case (you WANT the null to be true). Basically, when running a deviance test, the H0 states that the logistic regression model is the right model for the data.

What are the two types of misclassification?

Differential - generally unknown direction of bias Non-differential - generally biases toward the null

How is Lepto transmitted?

Direct (abraded skin), indirect (ingestion, aerosols)

How do you convert odds to probability?

Divide the odds by 1 plus the odds Odds = 1/9 = 0.111 0.111/1.111 = 0.1 or 10% probability

How do you convert probability to odds?

Divide the probability by 1 minus that probability i.e. probability of 10% = 0.10 odds are 0.1/0.9 = 1:9 or 0.111

A study (analytic, observational) has been conducted in which the sample size was adequate and bias has been controlled. Now, if the relative risk of association between a risk factor and the disease is equal to or less than one; A. There is no association between the factor and the disease B. The factor protects against development of the disease C. Either the matching or randomization has been unsuccessful D. The comparison group used was unsuitable and a valid comparison is not possible E. There is either no association or a negative association between the factor and the disease

E. There is either no association or a negative association between the factor and the disease (must account for both 1 which is the null and less than one)

What is secondary prevention?

Early detection, screening, and management of disease prior to clinical disease occuring

A _______________ study examines relationship between exposure and disease with a population level rather than individual level data

Ecological

In a ____________ study, characteristics of a group (not individuals) are examined (findings don't necessarily apply to outside populations or even individuals within the group)

Ecological study

____________ _______________ is when an association between exposure and disease is different for different levels of a third variable

Effect modification In other words, the effect of the exposure on the disease is modified by the third variable

_____________ is the extent to which an intervention, procedure, regimen, or service, when used in routine situations, does what it is intended to do

Effectiveness

____________ is the extent to which an intervention, procedure, regimen, or service, produces beneficial results under ideal conditions

Efficacy

________________ is the effects or end results achieved in relation to effort expended in terms of money, resources, and time

Efficiency i.e. cost benefit of interventions

What is the primary goal of randomization?

Eliminating selection bias

Describe how an epidemiological curve would look for an endemic disease

Endemic disease tends to fluctuate a bit but stay below a particular level (as in the left half of the graph shown)

What clinical sign groupings does Porcine Hemagglutinating Encephalomyelitis virus (PHEV) cause (3)?

Enteric (pigs <3 weeks old; inappetence, vomiting, stunted) CNS (piglets, ataxia, paralysis, paddling) Rarely respiratory (possible d/t PHEV in older but naive swine, atypical form of disease, or increased virulence of strain)

_____________________ is the study of dynamics of health and disease determinants in a population with the goal of prevention

Epidemiology

What is the causative agent of Equine Herpesvirus Myeloencephalopathy?

Equine Herpesvirus 1 or 4

Equine herpesvirus Myeloencephalopathy is caused by ....?.

Equine herpes virus 1

selecting study participants with only one level of the confounding variable (as all have the same level any effects of this variable are excluded) is what way of controling for confounding?

Exclusion

What are three ways to control for confounding?

Exclusion Matching Analysis (stratification)

To prove causation, what must be true regarding experimentation?

Experimental evidence that intervention prevented disease Experimentation may provide support for the causal hypothesis

What is R^2 represent when looking at a multiple regression line (3)?

Explained variation/Total variation provides a quantitative measure of how well the fitted model predicts Y Value is between 0 and 1, closer to 1 means the points are closer to the line, so a better fit

An odds ratio equal to 1 means what?

Exposure has no effect

To prove causation, what must be true regarding strength of association?

Exposure is more common in disease

An odds ratio of >1 means what?

Exposure is positively assocaited

To prove causation, what must be true regarding temporal sequence?

Exposure must precede disease

(External/Internal) validity is the ability of study results to be extrapolated to a target population

External

Hypothesis testing for the ratio of two population variances follows what distribution?

F distribution

When doing multiple regression, what test would you use to determine if if the entire set of independent variables (X1, X2...Xk) contribute significantly to the prediction of Y?

F test

What test could you run (2) if you wanted to test if there was a linear relationship between X and Y (and therefore the linear regression model would be a good fit)?

F test or t Test

What type of study is an economical approach to study the effects of two or more independent treatments?

Factorial Study design

What is a type II error?

Failing to reject the null hypothesis when in reality it is false

(T/F) 1 minus the p value is the probability that the alternative hypothesis is true

False

(T/F) Distributions that have larger standard deviations have more observations that are close to the mean

False

(T/F) Random sampling technique maximizes bias

False

(T/F) The p-value is the probability that the null hypothesis is true

False

(T/F) When p < 0.05 the null hypothesis is false

False

(T/F) When p > 0.05 there is no effect

False

(T/F) You can change numeric data to nominal or ordinal data, and vice versa

False Can change numeric (i.e. ages) into nominal or ordinal (i.e. age groups 0-2, 3-5, 6-8, etc) but can't go from groups back to nominal (typically the exact values aren't known, just where they fell in the group)

(T/F) If you are using linear/multiple regression, you can calculate the predicted value for any combination of X1 and X2

False Technically, YES you can plug and chug any numbers into the formula, but really, the model should only be used to calculate a reasonable combination of X1 and X2, so values that fall within the range of the data set used to create the model. Example, if you used age data as a variable and had years 15 - 65 included in your data set, you shouldn't be using the model created from that data to predict what will happen at age 95.

(T/F) There is a licensed vaccine in the United States for Rabbit Hemorrhage Disease Virus 2 (RHDV2)

False There are two vaccines licensed in the EU though

(T/F) A characteristic of the Poisson distribution is that only two outcomes are possible at each trial

False (this is true for binomial)

(T/F) If the 95% confidence interval includes 1 for the OR or RR it is statistically significant

False - 1 is the null value for a RR or OR so, because the CI contains this value, it is not statistically significant

(T/F) Contagious Equine Metritis is endemic to the US

False - FAD

(T/F) equine piroplasmosis is considered an endemic disease to the US

False - FAD, was eradicated from FL in the 1980s

(T/F) Relative Risk is calculated from prevalence data

False - INCIDENCE data!

(T/F) The normal probability model is most useful for situations with discrete-valued random variables

False - Poisson would be best Probability model is used for continuous, not discrete variables

(T/F) Rabbit Hemorrhage Disease Virus 2 (RHDV2) only affects domestic rabbits in North America

False - both domestic and wild rabbits

(T/F) The normal distribution depends on both both µ and 𝝀

False - both µ and sigma

(T/F) Randomization is a possible way to control for confounding in observational studies

False - can't use in observational studies

(T/F) Prevalence can be measured in a case control study

False - cannot measure incidence or prevalence because the number of cases and controls is fixed.

(T/F) Potential risk factors should be included as part of your case definition

False - do not include them

(T/F) In linear regression, Y is binary

False - in linear regression Y is a continuous number

(T/F) When gathering data for an outbreak investigation, a standardized questionnaire should be developed to include demographics, lab data, and risk factors or relevant exposures should be included, but NOT open ended questions

False - include open ended questions

(T/F) Surveillance is essentially limited to testing

False - involves data interpretation and analysis and a RESPONSE when a case/positive is found

(T/F) If a study has an inadequate sample size, then a result with a null finding (no statistically significant association detected) is still valuable

False - it is uninformative A true lack of association is difficult or impossible to distinguish from a true association that cannot be detected statistically because of inadequate power

(T/F) Failing to reject the null hypothesis means that the null hypothesis is true

False - may not have been able to detect the difference

(T/F) Animals can continue to spread Vesicular Stomatitis Virus to each other after the lesions have healed by aerosols

False - no animal to animal spread once lesions are healed

(T/F) A statistically significant result is also clinically/biologically significant

False - not always!

(T/F) There has never been an outbreak of Rabbit Hemorrhage Disease Virus 2 (RHDV2) in the United States

False - outbreak in 2020 affected not only the US but also Norway, Senegal, China, Iceland, Mexico, Nigeria and Singapore

(T/F) Non-parametric tests have the assumption of normality

False - parametric tests assume normality, non-parametric tests do no

(T/F) Vesicular Stomatitis Virus has been eradicated from the US

False - periodically reported in SE and SW US

(T/F) EHV-1 vaccine is available and labeled for both prevention of the respiratory and myeloencephalopathy forms of equine herpes virus

False - respiratory form only

(T/F) PPV and NPV are test characteristics and do not vary, but sensitivity and specificity are affected by prevalence of disease

False - reverse is true, PPV/NPV are affected by prevalence, and specificity and sensitivity don't change

(T/F) Lepto is shed in nasal and oral secretions (aerosols)

False - shed in urine and vaginal discharges

(T/F) True effect modification is extremely common because it is an artifact of the data, but confounding usually represents a biologic phenomenon and is much less common

False - should be rewritten Confounding is extremely common because it is an artifact of the data, but true effect modification usually represents a biologic phenomenon and is much less common

(T/F) Coefficients in logistic regression show causation

False - show association, NOT causation Two variables may have a relationship but may not be causal (i.e. increased drowning and ice cream production in the summer)

(T/F) You conduct an ANVOA on a set of population means and find they are different. You would like to to see which populations specifically differ, so you must conduct additional testing. You can run a t test to compare population means in each pair

False - technically you CAN do this, but it is not advised as it will lead to more falsely significant differences at a fixed alpha. example. Suppose there are 10 populations and therefore 45 pairs. If alpha is set at 0.05 then 45(0.05)=2, which means two comparisons are likely to be significant by chance Better to run a Tukey multiple comparison procedure

(T/F) Selection bias is bias based on how information is collected for a study

False - that is information bias

(T/F) Information bias is bias based on who gets into a study

False - that is selection bias

(T/F) There are no chronic carriers of leptospirosis

False - there are

(T/F) If a Pearson correlation coefficient has a value of 0.98, this means the the variable has a very strong causative effect

False - there is a strong positive correlation. This does NOT conclude causation.

(T/F) There are no vaccines that exist for Leptospirosis in dogs

False - there's a vaccine

(T/F) Case control studies are bad for rare diseases

False - they are great for them

(T/F) Predictive values (PPV/NPV) are used to apply to populations beyond that in which they are established

False - they cannot be applied beyond the population in which they are established

(T/F) Cohort studies work well with rare diseases

False - they do not

(T/F) Cohort studies are typically conducted quickly

False - they take a long time (and there is loss to follow up)

(T/F) You use the risk ratio to measure risk in a case control study

False - use odds ratio because you didn't know the incidence in the exposed and non exposed because you started with diseased and non diseased cases. Use the odds ratio. Risk ratio is used in a cohort study because you do know incidence in this case

(T/F) In a cross-sectional study, incidence is assessed

False - you can assess prevalence, not incidence

(T/F) A case series involves a control/comparison group

False it does not

(T/F) Cross sectional studies are good for rare disease

False they are not

(T/F) Effect modification is a type of bias that should attempted to be eliminated in the study design

False! Effect modification is a "natural phenomenon" that exists independently of the study design

Who provides approval of vaccines and biologics in a outbreak/ animal disease response?

Federal animal health officials

What are some clinical signs of equine piroplasmosis?

Fever Lethargy Inappetence Anemia icterus colic weight loss exercise intolerance sudden death asymptomatic

Which "test" (court established in 1932) states for a study to be admissible in court, it must be sufficiently established to have gained general acceptance in the field in which it belongs?

Frye Test

What type of bacteria is Leptospira?

Gram negative, spirochete

What makes pigs a "mixing vessel" for influenza viruses?

Have both type of virus receptors preferred by avian influenza A and human influenza A

Rabbit Hemorrhage Disease Virus 2 (RHDV2) has high or low mortality?

High (60-90%)

What is the treatment for equine piroplasmosis?

High dose imidocarb

What are four things about Campylobacter that can be classified into the host part of the epidemiological triad?

Humans and many animal species are hosts Animals are sub-clinical carriers or get enteritis Humans get enteritis C. fetus causes bovine genital campylobaceriosis

How should sick rabbits be treated for Rabbit Hemorrhage Disease Virus 2 (RHDV2)?

ISOLATE to prevent contact with other rabbits Plasma transfusion (increases clotting factors) IV fluids, handfeeding Note: recovered animals may shed virus for months but doesn't cause chronic infection

If a data set follows a normal distribution __________% of observations will be within ONE standard deviation of the mean, ___________% within TWO standard deviations, and ___________% within THREE standard deviations

If a data set follows a normal distribution 68% of observations will be within ONE standard deviation of the mean, 95% within TWO standard deviations, and 99.7% within THREE standard deviations

If you are comparing the means of two populations you would use the ___________ , but when comparing >2 populations you would run the ____________

If you are comparing the means of two populations you would use the t-test, but when comparing >2 populations you would run the ANOVA

If your study's effect size is large you would need an estimated (small/large) sample size

If your study's effect size is large you would need an estimated small sample size

If your study's effect size is small you would need an estimated (small/large) sample size

If your study's effect size is small you would need an estimated large sample size

Give an example of an intrinsic host factor that may influence disease outcome/susceptibility/exposure

Immunity, age, gender, breed

In Linear Regression, the outcome variable is measured on a __________________ scale and the relationship between the outcome and predictor variable is a ____________ line

In Linear Regression, the outcome variable is measured on a continuous scale and the relationship between the outcome and predictor variable is a straight line

In an outbreak investigation, you would use a _________ study in an outbreak in a small, well-defined population, while you would use a ____________ study when the population at risk is NOT well defined

In an outbreak investigation, you would use a cohort study in an outbreak in a small, well-defined population, while you would use a case control study when the population at risk is NOT well defined

In randomized complete block designs, experimental units are sorted into _________________ groups called blocks, then treatments are assigned at random within the blocks. Each treatment is included _________ (number) in each block

In randomized complete block designs, experimental units are sorted into homogeneous groups called blocks, then treatments are assigned at random within the blocks. Each treatment is included once (number) in each block

When is the Odds Ratio a good estimate of the Relative Risk?

In rare disease, where RR is appx 1

In simple linear regression the independent variable is denoted as ________ and the dependent variable is denoted as _______

In simple linear regression the independent variable is denoted as X and the dependent variable is denoted as Y

The number of new cases of a disease that occur in a population over a particular period of time divided by The sum of all individuals during the length of time at risk of developing a disease Is the.....?

Incidence rate

The number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease, expressed in person-time (e.g., person-years) is known as.....?

Incident density

What are two things that can make your confidence interval wider?

Increased variability decreased level of confidence

How can Rabbit Hemorrhage Disease Virus 2 (RHDV2) be transmitted, generally?

Indirect contact (fur, meat, body fluids, dead carcasses, food, water, clothing, mechanical vectors) Direct contact (human, infected rabbits urine and feces)

What is the only population a diagnostic sensitivity applies to?

Infected or diseased population

Agent characteristics, likelihood of exposure, and the host's ability to act against agent mechanisms are all forces that influence what?

Infectious disease occurrence

What type of bias really impacts internal validity?

Information bias

______________ bias is systematic error in the collection of exposure or outcome data that results in a mistaken estimate of an exposure's effect on the risk of disease

Information bias

(External/Internal) validity is the ability of a study to measure what it intends to measures

Internal

What type of validity must you have to extrapolate to a different population than the study population?

Internal validity (if you're not measuring what you're thinking you're measuring, then there is nothing to extrapolate)

Explain why it would or would not be appropriate to estimate "relative risk" from a typical cohort study

It is appropriate to calculate RR from a cohort study. RR is calculated using incidence data which can be determined from a cohort study.

What is one assumption of the the Mantel-Haenszel Test regarding the confounding variable?

It is categorical, with the different categories defining the strata

What is beta in regards to error rate?

It is the false negative error rate or the probability of making a type II error

Define the p-value

It is the probability that a difference as large as the one observed was due to chance

What must be true of the dependent variable (Y) in order to logistic regression?

It must be binary taking on only two values, often coded as 0 and 1

What type of curve is produced for survival analysis?

Kaplan-Meier

The ______________ statistic measures observer agreement beyond what we would expect by chance alone

Kappa statistic

If you are comparing the mean between more than two groups of nonparametric data, what test would you use?

Kruskal-Wallis ANOVA by ranks

If you have a several samples of means or medians and want to run a non-parametric test, what would you run?

Kruskal-Wallis ANOVA for ranks

______________ the numerical measure of the shape of data, and a normal distribution has a value of 0

Kurtosis Kurtosis >3 is sharp peak/heavy tail Kurtosis <-3 is flat peak with lighter tail

If you wanted a small p-value and a high power study, what sample size (generally speaking) would you need?

Large

When is the typical time of year that Leptospirosis cases increase?

Late summer and fall

What is the median survival time?

Length of time half the study population survives Note: don't need to observe all deaths, and less affected by outliers than the mean

If you want to make inference about the relationship between two quantitative variables, what test could you run?

Linear regression

The Pearson product moment (r) or population (p) correlation coefficient measures the strength of the ___________ relationship between X and Y, and ranges from -1 to +1

Linear relationship (can't use for non linear relationships)

If you wish to compare the survival experience of two groups, exposed and unexposed, what test would you use?

Logrank test (an application of the Mantel-Haenzel test procedure) Alternative procedures include Breslow test and Tarone-Ware test

You are conducting a study with a potential confounding variable, and you would like to control for it. You stratify your data according to this variable, so that you can then test your hypothesis. What statistical test should you perform?

Mantel-Haenszel Test

Equalizing the frequency of the confounding variable in the groups being compared is what way to control for confounding?

Matching

If you are comparing proportions that are paired or matched, i.e. asking the same group of people their political party allegiance before and after a TV commercial, what test could you use?

McNemar test

If you have matched pair samples of proportions, what test would you run?

McNemar's chi-square or one sample z-test

How do you calculate the third quartile or 75th percentile?

Median of the upper half of the observations

What type of study design provides the best strength of evidence?

Meta analyses (multiple results from a number of randomized clinical trials)

______________ bias occurs when either exposure or disease outcome is incorrectly classified (cases are classified as controls or controls as cases, etc)

Misclassification

____________ is ongoing observations without taking an action based on the outcome

Monitoring

How do you calculate cumulative probabilities? I.e. how would you calculate the cumulative probability of surviving a disease for two years, given the probability of survival for 0-1 year, then 1-2 years?

Multiply them Example. Survival from year 0-1 is 0.83, survival from year 1-2 is 0.78. Therefore, the cumulative probability to survival to year 2 is the probability of survival to year 1 multiplied by the probability of survival to year 2 given survival of year 1 = 0.83 x 0.78 = 0.65

If Factor A and Factor A only causes a disease, what type of casual relationship is this?

Necessary and sufficient

If Factor A, Factor B, and Factor together cause a disease, what type of causal relationship would Factor A considered to be?

Necessary but not sufficient

How is Rabbit Hemorrhage Disease Virus 2 (RHDV2) diagnosed?

Necropsy and PCR PCR confirms (use organs like liver, urine, feces and/or sera)

(Positive/Negative) predictive value will increase with an decrease of disease prevalence

Negative predictive value

Highly sensitive tests increase _________ and increase our confidence that a test negative subject is not affected

Negative predictive value

The ___________ is the fraction of test negative subjects that are truly NOT affected

Negative predictive value

What value answers the question, "how confident am I that a negative test indicates absence of infection/disease?"

Negative predictive value

__________ answers the question, if the test result is negative, what is the probability that this patient does not have the disease?

Negative predictive value

_________________ is the likelihood of not having the disease among those with a negative test

Negative predictive value

If Factor A + Factor B, Factor C + Factor D, or Factor E + Factor F will lead to a disease, what type of causal relationship does Factor A have?

Neither sufficient nor necessary

What type of data can be sorted and counted, and "assigned" numbers. Examples include letters, string, words, text

Nominal

What type of data can be used to compare an observed proportional distribution to an expected distribution?

Nominal data

What are some clinical signs of lepto?

Non specific (fever, myalgia), that progresses to renal disease, hepatic disease, and reproductive dysfunction

Which type of misclassification biases toward the null?

Non-differential

_______ bias is when subjects deferentially do not participate

Non-response

The ___________ distribution can be used to approximate the Poisson distribution for large values of λ (average number of success in a given period).

Normal -Mean=µ= λ -Variance = σ^2 =λ

What does it mean if the R0 is > 1?

Number of cases increasing - leading to an epidemic or pandemic which may or may not be followed by an endemic situation

What does an R0 = 1 mean?

Number of cases is staying the same (endemic situation)

What type of data can be mathematically handled (i.e. averaged, standard deviation, etc)?

Numerical (i.e. numbers...)

A _______________ study studies causes, prevention, and treatments for disease. Investigator passively observes as nature takes its course.

Observational

Cohort, case-control, cross-sectional, case series, and case report studies are all what type of study design?

Observational

In logistic regression, the formula for the odds ratio in favor of disease for A versus B is....?

Odds of A / Odds of B or if Y is coded 1 for disease and 0 for no disease, then OR = e^Bj (Bj being the coefficient of x)

What is one measure of risk that can be used in cohort studies, case-control studies, AND cross sectional studies?

Odds ratio

What is the common test statistic in a case-control study?

Odds ratio

US Preventive Services Task Force (USPSTF) makes suggestions for clinical services/tests to be provided in practice using various grades (A through I). What are the suggestions for a service rated Grade C?

Offer to provide this service only if there are other considerations that support the offering or providing the service in an individual patient

To prove causation, what should be true specificity of association?

One exposure = one disease It is easier to demonstrate support for causation when associations are specific

Define selection bias

One relevant group in the population (such as exposed cases) has a higher probability of being included in the study sample

What is are two examples of point source transmission?

Oral (waterborne or foodborne) Direct contact

Where are vesicles typically found in Vesicular Stomatitis Virus (5)?

Oral cavity Lips Nose Teats Coronary bands

A _______________ is an epidemic that affects several countries or continents

Pandemic

(Parametric/Nonparametric) distributions are symmetrical around the mean (bell-shaped)

Parametric

What are the two groups of probability distributions?

Parametric ("normal") Nonparametric

(Parametric/Nonparametric) tests make distributional assumptions about the population from which the sample was drawn while (Parametric/Nonparametric) makes no such assumptions

Parametric tests make distributional assumptions about the population from which the sample was drawn while Non-parametric makes no such assumptions

The _________ is used to estimate the population correlation coefficient. This ranges from -1 ( a perfect negative relationship) to +1 ( a perfect positive relationship). A value of 0 indicates no linear relationship.

Pearson correlation coefficient

If you are looking for an association/correlation (not a difference) for parametric data what test would you use?

Pearson product moment (r)

The proportion of the population with a specific disease over a given period of time (e.g., a specific month or specific year) is known as...?

Period prevalence

The number of cases of a disease present in the population at a specific time divided by the total number of persons in the population at that specific time is known as .... ?

Point prevalence

The ________ distribution is employed when counts are made of events during a given time period

Poisson i.e. number of return visits within 72 hrs to the ER

Influenza like illness in pigs is suggestive of Influenza A virus, but also what other two viruses?

Porcine reproductive and respiratory syndrome virus (PRRSV) rarely: Porcine Hemagglutinating Encephalomyelitis virus (PHEV)

In the infectious disease chain of transmission, what two things contribute to the susceptibility of the host?

Portal of entry Innate characteristics of the host

In the infectious disease chain of transmission, what two things contribute to the means of disease transmission?

Portal of exit Mode of transmission

If a clinician wants to known how to interpret test results when a disease status is unknown, what tests are used?

Positive and Negative predictive values

(Positive/Negative) predictive value will increase with an increase of disease prevalence

Positive predictive value

The _______________ is the fraction of test positive subjects that are truly affected

Positive predictive value

What value answers the question, "how confident am I that the positive test indicates infection/disease?"

Positive predictive value

_____________ answers the question, if the test results are positive for this patient, what is the probability that this patient has the disease?

Positive predictive value

______________ is the likelihood of having the disease among those with a positive test

Positive predictive value

___________ is the probability of correctly rejecting the null hypothesis

Power (1-Beta)

The __________ is the "true positive" fraction of population

Prevalence

The ___________ is the fraction of a defined population that has some characteristic at a given point in time

Prevalence

___________ measures the probability of being affected/infected with a disease/pathogen

Prevalence

What are two measures to evaluated in a cross-sectional study?

Prevalence Odds or risk ratio

What is the difference between prevalence and incidence?

Prevalence = (# of CURRENT cases)/(population at risk) - is at a given point in time Incidence = (# of NEWLY affected cases)/(population at risk) - is at a specific period in time

What is an equation that relates prevalence and incidence?

Prevalence = Incidence x Duration

If your sample size to detect at least 1 case of disease with expected 1/100,000 prevalence at slaughter with high confidence (95%) was 300,000, and you found zero positives in 300,000 samples of a high risk sub population, what can you say about prevalence?

Prevalence in this sub population is <1 in 100,000 with 95% confidence

(Incidence/Prevalence) is can be described as the burden of disease, while (incidence/prevalence) can be described as the probability of becoming a case

Prevalence is can be described as the burden of disease, while incidence can be described as the probability of becoming a case

Positive and Negative predictive value are affected by what two things?

Prevalence of disease Specificity of test

What is primary prevention?

Prevention that precedes the development of disease and includes education about health promotion activities, immunizations, wearing protective devices to prevent injury

Malaria prophylaxis during travel to an area where malaria is endemic is an example of _______________ prevention

Primary

___________ prevention is intended to reduce new occurrences of disease

Primary

What is the difference between a primary case and secondary case in a disease outbreak?

Primary = disease from source Secondary case = disease from primary case

What are the species primary effected by Vesicular Stomatitis Virus?

Primary: Horses, cattle, swine Others: sheep, goats, camelids, wildlife and humans

What is the difference between primary and secondary data?

Primary: collected for the first time by the researcher Secondary: Information previously collected for other purposes (I.e. ref lab test results)

An epidemiological curve with two "peaks" could be considered what type of curve?

Propagating

To prove causation, what must be true regarding both coherence with established facts and biological plausibility?

Proposed causal mechanism should be plausible An association is more likely to be causal if it is biologically sensisble

What are two pros and two cons associated with secondary data?

Pros: cheap and easy Cons: may lack in quality/accuracy, may not have all the info needed to answer a specific question

What are two pros and two cons associated with primary data?

Pros: current, accurate, answers specific question Cons: expensive and time consuming

____________ ________________ is an organized community effort to prevent disease and promote health

Public Health

What is triangulation?

Pulling all the evidence together to see if it points in the same direction

In zones of response, the buffer zone surrounds what area?

Quarantine

The average number of secondary infections caused by a single typical infected individual among a completely susceptible population is defined as the....?

R0 or basic reproductive ratio

What is a better measure of strength than the correlation coefficient (r)?

R^2

What value is interpreted as the amount of variance in one variable that is accounted for by knowing the second variable, i.e. A explains xx% of B?

R^2 example: r = 0.9, r^2 = 0.81 = 81% A explains 81% of B

What are the three ways to control for confounding in the study design?

Randomization, restriction, and matching

A case control study is good for (common/rare) outcomes

Rare

A case control study is more desirable when the disease of interest is (common/rare)

Rare

What is the odds ratio, mathematically?

Ratio of odds of disease in the exposed group to the odds of disease in the unexposed group OR = odds(D+|E+)/odds(D+|E-)

Define Relative Risk or the Risk Ratio, mathematically

Ratio of risk of disease in the exposed group to the risk of disease in the non-exposed group

To prove causation, what must be true regarding consistency of effect?

Relationships demonstrated in multiple studies are more likely to be causal - Strength of association may differ, but direction should be the same

The incidence rate among exposed divided by The incidence rate among unexposed Is known as the .....?

Relative Risk

How the association between exposure and outcome of interest measured in a cohort study?

Relative risk

__________ _____________ measures the association between exposure to a particular factor and risk of a health outcome

Relative risk

A ____________ is an ecological nice where a pathogen lives and multiples and generally needed to perpetuate the agent

Reservoir

_____________ _______________ result from recall bias and other issues with recall

Respondent errors

What are two options for approaching active surveillance?

Risk based: sampling where population is categorized as either high-risk or low-risk Population based: no regard to risk grouping

What is the difference between a risk ratio and a rate ratio?

Risk ratio: ratio between cumulative incidences (risk in exposed divided by risk in unexposed) Rate ratio: Ratio between two incidence densities (rate in the exposed divided by the rate in the unexposed)

In addition to vesicles, what are other clinical signs seen with Vesicular Stomatitis Virus?

Salivation, anorexia, weight loss secondary to oral lesions Lameness with coronary band lesions

What is an example of lead time bias?

Screening to detect a disease earlier - could make it look like there is an increased survival time, but in reality patient is dying at the same point, but you detected the disease earlier on so it LOOKS like they survived a longer period of time.

____________ bias can occur whenever identification of individual subjects for inclusion results in mistaken estimate of the measure of effect

Selection

A case control study is prone to what type of bias?

Selection bias

What type of bias really impacts external validity?

Selection bias

What are the two major categories of Bias?

Selection bias Information bias

_____ bias is when subjects deferentially self refer

Self-selection

The ability to find true positives based on a single biologic sample take at a point in time is defined as the ?

Sensitivity

Sequential testing (increases/decreases) sensitivity and (increases/decreases) specificity

Sequential testing decreases sensitivity and increases specificity

Name at least three test types that can be used to diagnose Brucella canis

Serology: Rapid slide aggultination test (RSAT), Tube agglutination test (TAT), 2-mercaptoethanol (2-ME), Agar gel immunodiffusion assay (AGID) PCR - uncommon, but used to identify to genus level

What are four tests that can test your numerical data for normality?

Shapiro-Wilk Kolmogorov-Smirnov Anderson-Darling Skewness-kurtosis or D'Agnostinio-Pearson

To prove causation, what should be true regarding analogy?

Similar evidence between another exposure-disease relationship Similar evidence can provide support for a causal association

Simultaneous testing (increases/decreases) sensitivity and (increases/decreases) specificity

Simultaneous testing increases sensitivity and decreases specificity

In what type of data (symmetric or skewed) would quartile 1 and quartile 3 be a good measure for spread?

Skewed (SD and min/max is good for symmetric data)

Define misclassification or information bias

Some degree of misclassification of the exposure information exists in both cases and controls, but one group tends to mistakenly report to a greater extent I.e. unexposed cases tend to mistakenly report past exposure to a greater extent than do controls

If you are looking for an association/correlation (not a difference) for nonparametric or ordinal data what test would you use?

Spearman rank (rho)

If you have nonparametric data on at least the ordinal scale, what correlation coefficient do you use to estimate the population correlation coefficient?

Spearman rank-correlation coefficient

The _______________ of a test is the likelihood of a negative test among those without the disease

Specificity

The ability to find true negatives based on a single biologic sample taken at a point in time is defined as the ?

Specificity

How do you measure years of potential life lost?

Standard age of death (i.e. 75 years in US) minus age at which the individual died = years of life lost (then sum total all individuals for total life years lost) Note: can't be negative. I.e. 75-80 = 0 for life years lost

Observed number of deaths compared to the total number of deaths expected is known as the ..... ?

Standardized mortality ratio

What are two ways to control for confounding in the study analysis?

Stratification and multivariate analysis

With ___________ _____________ sampling, the population is divided into various subgroups with similar characteristics, and then a sample is randomly selected from each subgroup proportionate to their number in the overall population

Stratified random sampling

If either Factor A, factor B, or Factor C can cause disease, what type of causal relationship does Factor A have?

Sufficient, but not necessary

When evaluating a confidence interval for the difference between two population means, if the interval contains only negative numbers, what does this suggest?

Suggests that mean of population 1 is smaller than population 2 (m1 - m2 = negative) Conversely, if it the CI was only positives, you could conclude that the mean of pop 1 was LARGER than pop 2

When do Vesicular Stomatitis Virus outbreaks tend to occur?

Summer months cluster along river drainages (insect vectors)

What is the treatment for Equine Herpesvirus Myeloencephalopathy (2)?

Supportive care Antivirals (Death often by euthanasia)

What is the treatment for Leptospirosis?

Supportive care and antimicrobials

________ is a focused assessment with a specific aim or goal - similar to a cross-sectional epidemiological study

Survey

If you wanted to analyze time-to-event data, what test could you run?

Survival analysis

What are the three classification of cases in an outbreak investigation?

Suspect Presumptive positive Confirmed positive

What are 3 things that will help you develop a specific case definition?

Symptoms/lab results Time Period Location

Name at least three signs or symptoms of Rabbit Hemorrhage Disease Virus 2 (RHDV2)

Symptoms: Loss of appetitie, lethargy, fever (12-26hrs), siezures, dyspnea, DEATH, hemorrhage in the eyes, bleeding from moust/rectum, vocalization, sudden death

What are two types of interactions (combined effect of two predictor variables)

Synergistic - presence of both predictor variables potentiates the effect (2+2 = 6) Antagonistic - Presence of both predictor variables diminishes or eliminates the effect (2+2=1)

______________ error is biases due to the way in which subjects have been selected (selection bias), the way study variables are measured (information bias), and confounders that are not completely controlled for

Systematic error

___________ sampling technique assumes that the population list is randomly distributed and uses the list to select the sample at fixed intervals

Systematic sampling (i.e. sample every fourth person)

How do you calculate the true positive rate? The false positive rate?

TPR = sensitivity = TP/(TP+FN) FPR = 1 - Specificity = 1 - (TN/(TN+FP))

Given the variance, how do you calculate the standard deviation?

Take the square root of the variance

What is the causative agent of Contagious Equine Metritis?

Taylorella equigenitalis

Monitoring glucose levels in patients with diabetes to prevent complications is an example of _____________ prevention

Tertiary

______________ prevention is conducted at the clinical stage of disease

Tertiary

______________ prevention is intended to reduce complications and disabilities due to disease

Tertiary

The probability that a test will correctly classify truly diseased individuals is known as ?

Test sensitivity

The probability that the test will correctly classify truly non-diseased individuals is known as?

Test specificity

Testing in parallel increases (sensitivity/specificity) but decreases (sensitivity/specificity)

Testing in parallel increases sensitivity but decreases specificity

Testing in series increases (sensitivity/specificity) but decreases (sensitivity/specificity)

Testing in series increases specificity but decreases sensitivity

A large R^2 doesn't necessarily mean the fitted model is useful in multiple regression. Why?

The MSE (estimate of variance) may still be too large for inferences to be useful

In the formula Y = β0 + β1X1 + ...+ βkXk + ε, what does β0 represent?

The Y intercept The log odds of the probability of disease if all predictor variables are absent/=0 (aka, getting the disease in absence of all the variables accounted for)

If you are given an even set of values, how would you calculate the median?

The average of the two middle values i.e. 1 ,3,5,7,8,9 (5+7)/2 = 6

What is the R0?

The basic reproduction rate/ratio The average number of new cases of infection caused by one typical infected individual, in a population consisting of susceptibles only

How is relative risk calculated?

The cumulative incidence of disease in exposed animals ( A/(A+B) ) divided by the cumulative incidence of disease in unexposed animals ( C/(C+D) )

In the formula Y = β0 + β1X1 + ...+ βkXk + ε, what does ε represent?

The error term Accounts for the variability between individual data points and mean

In the infectious disease chain of transmission, what two things contribute to the source of the infection?

The etiologic agent itself Reservoir

What is alpha in regards to error rate?

The false positive error rate, or the probability of making a Type 1 error

The ___________ and the _____________ of the Poisson distribution are both equal to λ (average number of success in a given period)

The mean and the variance of the Poisson distribution are both equal to λ (average number of success in a given period)

When evaluating a confidence interval for the difference between two population means, if the interval contains 0, what does this suggest?

The mean of the two populations are equal

What does an R0 of < 1 mean?

The number of cases is decreasing - leading to the end of an epidemic or disappearance of a previously endemic disease

How do you calculate the odds ratio?

The odds of being a case with the risk factor divided by The odds of being a case without the risk factor Standard 2x2 values = (a/b) / (c/d) = (a*d)/(b*c)

The (odds ratio/relative risk) is used in a case control study, while the (odds ratio/relative risk) is used in a prospective cohort study

The odds ratio is used in a case control study, while the relative risk is used in a prospective cohort study Note: the odds ratio approaches the risk ratio with rare outcomes

In logistic regression, the odds in favor of getting a disease for group A is mathematically....

The probability of getting disease for A divided by one minus the probability of getting the disease for A

In logistic regression, the odds in favor of getting a disease for group B is mathematically....

The probability of getting disease for B divided by one minus the probability of getting the disease for B

If the disease is rare, the odds ratio is approximately equal to .....?

The risk ratio

What is epidemiology?

The study of the dynamics of health and disease determinants in a population with the goal of prevention

In the formula Y = β0 + β1X1 + ...+ βkXk + ε, what does Y represent?

The value of the outcome given the values of the predictor variable(s)

What is tertiary prevention?

Therapy, or measures taken to manage a disease from progressing or improving survivorship after clinical disease has occurred

If your beta is set at 0.1, what does this mean in words?

There is a 10% chance of missing an association between variables

How are controls selected in a case control study?

They are sampled (randomly) from the entire source population that gave rise to the cases, and classified according to exposure

How is equine piroplasmosis spread (3)?

Ticks Exposure to infected blood or blood products Vertical (possible, but not efficient)

What variable can be used to determine exposure period, predict course of the epidemic, and suggest the type of epidemic?

Time

What is the goal of a case control study?

To determine if the outcome of interest is associated with exposure

What is the purpose of surveillance?

To provide information for action (institute or modify control, eradication and preventive measures. Evaluate previous efforts)

In an ANOVA, the __________ measures total variability of the observations around the overall mean

Total sum of squares (SST) (note: if it's small then all numbers are close and the dataset is flat)

Non compliance in a study, if similar in both groups observed, will move the results further (toward/away) the null hypothesis

Toward

(T/F) 5.A p-value, or statistical significance, does not measure the size of an effect or the importance of a result.

True

(T/F) A characteristic of a binomial model is that only two outcomes are possible at each trial

True

(T/F) An increase in either sensitivity or specificity often corresponds to a decrease in the other

True

(T/F) An odds ratio can be used in case-control studies

True

(T/F) An outbreak or epidemic is an increase in the number of cases over expected in a given time period

True

(T/F) Canicola, Icterohaemorrhagiae, Autumnalis, Pomona, Grippotyphosa, Bratislava are all serovars of Lepto

True

(T/F) Confounding results in a mistaken estimate of an exposure's effect on the risk of disease

True

(T/F) Coxiella burnetti has been identified in placentas of Norther Fur Seals

True

(T/F) Discrete variables are numerical values you can list or count

True

(T/F) Equine Herpesvirus Myeloencephalopathy can be caused by either the wild type strain or the neuropathogenic strain

True

(T/F) For poultry farms experiencing a high path AI outbreak, having a high degree of in-company connectedness with other farms, that is common feed trucks, company personnel, and common rendering trucks coming on site, increases their exposure risk

True

(T/F) Functions of the field epidemiologist include investigating potential disease problems, monitoring surveillance programs, providing education, participating in data collection and the dissemination of information

True

(T/F) Having multiple controls for one case may increase the power of a study up to a 4 to 1 ratio

True

(T/F) If you restrict your study population to one group, then the variable that might be a confounder is no longer an issue

True

(T/F) In a normal distribution, the mean, median, and mode are all equal

True

(T/F) In logistic regression, y is a binary

True

(T/F) It is important to known why some animals or people are more likely to get sick than others in a disease outbreak, because we can target prevention at these individuals

True

(T/F) It is not necessary to vaccinate everybody in a population to eliminate an infection. The susceptibles can be protected by virtue of their association with vaccinates ("herd immunity")

True

(T/F) Leptospirosis can cause meningitis in humans

True

(T/F) Leptospirosis is distributed worldwide

True

(T/F) Leptospirosis persists in urban areas

True

(T/F) More than mere presence of the agent (i.e. virus, bacteria, fungus, etc) is necessary for infectious disease to occur

True

(T/F) Odds ratio can be used to measure association between exposure and outcome in a cross sectional study

True

(T/F) Porcine Hemagglutinating Encephalomyelitis virus (PHEV) is endemic in swine herds throughout the world and passive maternal immunity provides protection

True

(T/F) Predictive values (PPV/NPV) are closely related to prevalence of disease in the population

True

(T/F) Rabbit Hemorrhage Disease Virus 2 (RHDV2) survives freezing

True

(T/F) Rabbit Hemorrhage Disease Virus 2 (RHDV2) vaccines that are licensed in the EU may be used in the US under special permit.

True

(T/F) Randomization increases the likelihood that groups will be comparable in both recognized and unrecognized variables

True

(T/F) Stallions show no clinical signs when infected with Taylorella equigenitalis

True

(T/F) Steps for an outbreak investigation may occur simultaneously or be repeated as new information is received

True

(T/F) The Mantel-Haenszel Test can be applied for both retrospective and prospective studies

True

(T/F) The Poisson distribution depends on 𝝀

True

(T/F) The Wilcoxon signed-rank test is not affected by outliers

True

(T/F) The correlation coefficient (r) is highly sensitive to extreme points/ outliers

True

(T/F) The mean can be thought of as the balancing point of a distribution of data

True

(T/F) The median cuts a distribution down the middle, so about 50% of the observation are below it and about 50% are above it

True

(T/F) The odds ratio is a common test statistic for the cohort study

True

(T/F) The shape of a binomial distribution depends on both n and p

True

(T/F) Unlike other types of bias, confounding can sometimes be eliminated during data analsysi

True

(T/F) Usually, a decrease in type one error is achieved at the expense of an increase in type II error

True

(T/F) When assessing causality, consideration of alternate explanations is important to report that alternative explanations (bias or confounding) have been considered

True

(T/F) With Rabbit Hemorrhage Disease Virus 2 (RHDV2) death usually occurs in 1-3 days and necropsy reveals hepatic necrosis and hemorrhage

True

(T/F) You usually continue disease testing or surveillance for some time after the last positive case in an outbreak

True

(T/F) equine piroplasmosis causes a life long infection of equids

True

(T/F) equine piroplasmosis testing is required for importation into the States

True

A characteristic of a Poisson distribution is that the mean equals the variance = 𝝀

True

(T/F) Prevalence is always an estimated parameter

True Usually based on imperfect diagnostic tests and limited sampling of the population

(T/F) Scientific conclusions and business or policy decisions should not be based only on whether a p value passes a specific threshold

True •A conclusion does not immediately become true if p < 0.05 or false otherwise.

(T/F) P values do not measure the probability that the studied hypothesis is true, or the probability that the data were produced by random chance alone

True •A p-value is a statement about the data in relation to H0, not a statement about the hypothesis.

(T/F) P values can indicate how incompatible the data are with a specified statistical model

True •Small p implies data are incompatible with H0 •Large p implies data are compatible with H0

(T/F) Cohorts may be closed, fixed, or dynamic

True Closed: no gains or losses Fixed: no gains, but losses can occur Dynamic: both gains and losses can occur

(T/F) Confounding can both cause an apparently strong association between exposure and outcome as well as mask an association

True (masking is less common)

(T/F) Cohort studies are good for proving causation

True (study is set up by dividing people into exposure groups before a disease occurs)

If you are evaluating the sensitivity and specificity of a test, what is assumed you already know?

True disease status

1 - the prevalence is the ?

True negative fraction of the population

What is the formula for specificity ?

True negatives / (True negatives + False positives) (or True negatives/all D-) (or d/(b+d) )

What is the difference between true prevalence and apparent prevalence?

True prevalence is the proportion of disease positive animals in the total population (D+/Total pop) Apparent prevalence is the proportion of test positive animals in the total population (T+/total pop)

What is the only population that a diagnostic specificity applies to?

Uninfected or non-diseased population

Give an example of an extrinsic host factor that may influence disease outcome/susceptibility/exposure

Use/occupation Diet Travel Behavior

What is blocking in regards to statistical testing, and when would it be used?

Used to control a nuisance source of variability, so it is used to eliminate these effects on comparisons among treatment groups. This is also known as a two way ANOVA i.e. Comparing teaching methods for patients to learn how to use a prosthetic device, and then blocking by age to control for this factor in rate of learning.

When assessing causality, a(n) _______________ ________________ shows that the if the factor causes the disease, the exposure to that factor must occur before the disease develops

When assessing causality, a Temporal Relationship shows that the if the factor causes the disease, the exposure to that factor must occur before the disease develops

When assessing causality, ______________ is when the findings should be consistent with existing biologic knowledge

When assessing causality, biologic plausibility is when the findings should be consistent with existing biologic knowledge

When assessing causality, ______________ shows that if a factor is a cause of a disease, we would expect the risk of disease to decline when exposure to the factor is reduced or eliminated

When assessing causality, cessation of exposure shows that if a factor is a cause of a disease, we would expect the risk of disease to decline when exposure to the factor is reduced or eliminated

When assessing causality, _____________________shows that as the dose of exposure increases, the risk of disease also increases.

When assessing causality, dose-response relationship shows that as the dose of exposure increases, the risk of disease also increases. Note: if present it is strong evidence for a causal relationship, but absence of a dose-response relationship does not rule out a causal relationship

When assessing causality, _____________________ is when you expect to see the same findings in different studies and in different populations

When assessing causality, replication of findings is when you expect to see the same findings in different studies and in different populations

When assessing causality, ______________ is when a certain exposure is associated with only one disease

When assessing causality, specificity of association is when a certain exposure is associated with only one disease

When assessing causality, _____________________ is measured by the relative risk or odds ratio.

When assessing causality, strength of association is measured by the relative risk or odds ratio. (Note: the stronger the association the more likely the relation is causal)

When comparing survival curves, a (vertical/horizontal) gap means that at a specific time point, one group had a higher survival rate. A (vertical/horizontal) gap means that it took longer for one group to experience a certain survival rate.

When comparing survival curves, a vertical gap means that at a specific time point, one group had a higher survival rate. A horizontal gap means that it took longer for one group to experience a certain survival rate.

When can the normal distribution be used as an approximation to the binomial distribution?

When n (trials) is large and/or p (probability of success) is close to 50%

If you are testing an animal for lepto and you suspect it is early in the course of disease, what is the best sample to collect and run?

Whole blood PCR - positive early in infection prior to seroconversion (urine is positive 7-14 days after infection)

If you are comparing two independent samples that are on the ordinal (or numerical) scale and assumption of normality is grossly violated, what test would you run?

Wilcoxon rank sum test (Mann Whitney U test) (This is analogous to the t test, which is used for normally distributed or parametric data)

If you are comparing the mean between two independent groups of nonparametric data, what test would you use?

Wilcoxon rank sum test (Mann-Whitney U)

The ______________ test can be useful to compare two independent groups when its inappropriate to assume normality and the sample size is small (<30)

Wilcoxon rank sum test (Mann-Whitney)

If you are comparing the mean between a single group with paired nonparametric data, what test would you use?

Wilcoxon sign rank test

If you have a sample of means or medians that are matched pairs, and want to run a non-parametric test, what test would you do?

Wilcoxon signed rank test

If you have one sample of means or medians, and you want to run a non-parametric test, what would it be?

Wilcoxon signed rank test

If the data you are analyzing is a paired sample study, but the assumptions of normality are grossly violated and the observed differences are on an ordinal (or numerical) scale, what test would you run?

Wilcoxon signed rank test (this is analogous to the paired t test, but for non normally distributed data)

The ____________ test can be useful to compare two dependent groups when its inappropriate to assume normality and the sample size is small (<30)

Wilcoxon signed-rank test

If you have two samples of means or medians, and you want to run a non-parametric test, what would it be?

Wilcoxon-Mann-Whitney rank sum test

When is a chi-square test used?

With nominal/proportional data - comparing observed proportional distribution to an expected distribution

What are three things about Campylobacter that can be classified into the Environment part of the epidemiological triad?

Worldwide Survives in moist environments Susceptible to most disinfectants

Name at least three things that you would place in the epidemiological triad under the "Environment" category for Q fever

Worldwide (except New Zealand) Relatively environmentally hardy Dust and wind Variable susceptibility to disinfectants

What is the formula for attack rate?

(# affected from risk group)/(total # in risk group)

What is the formula for true prevalence?

(Disease pos)/(Total population)

What is the mathematical formula for specificity?

(True Negatives) / (True Negatives + False Positives) Standard 2x2 table = D/(B+D)

What is the mathematical formula for Negative Predictive Value?

(True negatives) / (true negatives + False Negatives) Standard 2x2 table = D/(C+D)

How do you calculate test accuracy?

(True positives + True negatives) / (Total tested) (a+d) / (a+b+c+d) The proportion of the test results that are correct

What is the mathematical formula for sensitivity?

(True positives) / (True Positives + False Negatives) Standard 2x2 table = A/(A+C)

What is the formula for sensitivity?

(True positives)/(True positives + False negatives) (or True positives/all D+) (or a/( a+c) )

What is the the mathematical formula for Positive Predictive Value?

(True test and disease Pos) / (all test positives) Standard 2x2 table = A/(A+B)

How do you calculate relative risk?

(attack rate in group 1)/(attack rate in group 2)

How do you calculate the odds of an animal getting not getting a disease if it experienced exposure?

(number of animals who were exposed but disease negative) / (number of animals who were not exposed and are disease negative)

How do you calculate the odds of an animal getting a disease if it experienced an exposure

(number of animals with exposure and disease present) / (the number of animals unexposed animals with disease present) 2x2 formula (A) /(C)

What is the formula for apparent prevalence

(test positive)/(total population)

What is the formula for positive predictive value?

(true positives)/(all that test positive) a/(a+b)

What is the formula for net sensitivity and specificity for testing IN SERIES (sequentially)

-Net sensitivity=(sensitivity test 1*sensitivity test 2) -Net specificity= (specificity test 1+specificity test 2)-(specificity test 1*specificity test 2)

What is the formula for net sensitivity and specificity for testing IN PARALLEL (simultaneously)?

-Net sensitivity=(sensitivity test 1+sensitivity test 2)-(sensitivity test 1*sensitivity test 2) -Net specificity=(specificity test 1*specificity test 2)

What constitutes a foodborne outbreak?

-Two or more persons who have the same disease, similar symptoms, or excrete the same pathogens -Person/Place/Time association between the persons -Common food has been ingested

What is the range for an odds ratio?

0 to infinity

What is the range of the Risk Ratio?

0 to infinity

What value of the correlation coefficient (r) represents little or no relationship?

0-0.25

An Odds Ratio or Risk Ratio of what value would represent no association between the predictor variable and outcome of interest (aka the null hypothesis)

1

If you were evaluating the confidence interval comparing the ratio of two population variances, what number in the confidence interval would suggest the variances are equal?

1 (ratio of equal variances will =1)

What is the power of a test?

1-beta The probability of detecting a difference when one really exists (Min is usually 0.8)

To be a confounder, what two criteria must a variable meet?

1. Associated with the outcome (i.e. is a risk factor for the disease) 2. Associated with the exposure but is not a result of the exposure (i.e. is not on the causal pathway from exposure to outcome)

How do you calculate population attributable risk?

1. Calculate incidence in total population: [(incidence in those w/factor)(%of those with factor in population)] + [(incidence in those w/o factor)(% of those without factors in population)] 2. Population attributable risk = (incidence in total population (step 1) ) - (incidence in nonexposed group) (note: Percent as a decimal in this calculation)

What are two things to include in a key message for owners/public regarding campylobacter and pets?

1. Campy causes diarrhea in people, but many animals carry it without being sick - so quickly clean up accidents in house and wash hands immediately afterward 2. Known risks with feeding raw including salmonellosis and campybacteriosis which cause diarrhea in people. Make sure to clean and disinfect all surfaces/bowls used in food prep after dog has eaten, including floor.

What are three characteristics about Brucella canis in the environment, specifically?

1. Can persist up to 8 months or longer if colder 2. Susceptible to most commonly used disinfectants 3. Close contact likely contributes to transmission

What are two defining characteristics of a case-control study?

1. Compare individuals with disease (cases) to those without disease (controls) 2. Examine difference in exposure or risk factors

What are the three factors affecting the width of the confidence interval?

1. Confidence level 2. Sample size 3. Standard deviation

What are three requirements for surveillance?

1. Defined disease monitoring system 2. Predefined threshold for action 3. Predefined directed actions (responses)

What are four things to know that are important for calculating your sample size?

1. Desired values for the probabilities of alpha and beta 2. Expected magnitude of effect (RR or OR) 3. Baseline exposure or outcome rates 4. Formula (varies by study design)

What are four examples of selection bias?

1. Detection bias - persons followed more closely by health care providers because of some exposure are more likely to be diagnosed as a case 2. Self-selection bias - subjects deferentially self refer 3. Non-response bias - subjects deferentially do not participate 4. Inappropriate comparison group - comparison group does not appropriately represent the population from which cases arose

What are five advantages to active surveillance over passive surveillance?

1. Detects more cases 2. increased certainty of disease freedom 3. Prevalence estimate if cases are found 4. Lower likelihood of under reporting 5. More credible system for international trade

List at least four biosecurity practices to keep Rabbit Hemorrhage Disease Virus 2 (RHDV2) from spreading to a rabbitry or pet home

1. Do NOT feed foraged plants, grasses, tree branches 2. House rabbits indoors with no outdoor playtime 3. Wash hands thoroughly before handling 4. Change clothes and wash hands TWICE afte rhandling or contact with other rabbits 5. Use disinfectants 6. Quarantine any new rabbits at least 14 days 7. Do NOT touch dead animals 8. Know sources of hay and feed and whether they are grown in outbreak areas 9. Keep insects away from animal and feed areas

What 3 assumptions must be met when choosing to use the t test to compare two means?

1. Each group is normally distributed (test this) 2. The SD or variances are appx equal (sd1 should not be >/= sd2) 3. The groups are independent

What are the 3 steps in a case control study?

1. Find all the cases you can (outcome of interest) 2. Use a rule to select controls (from the same population as the cases, without outcome of interest) 3. Discover what fraction of cases and what fraction of controls were exposed to the risk factor of interest

You want to compare the difference in means between six populations. What statistical test or tests should you run (if multiple, what order?)

1. First run an ANOVA to see if the population means are different. If they are not, you can stop here. If they are, proceed to step 2. 2. Run a Tukey test to do a pairwise comparison of the population means to find out which pairs are significantly different. (Note: A Scheffe or Bonferroni test could also be done here, but for pairwise comparisons, Tukey provides narrow CIs and is superior to those tests)

What are 3 disadvantages to active surveillance over passive surveillance?

1. High cost per case detected 2. Must have clear description of purpose 3. Often takes a lot of time

When developing a questionnaire during an outbreak investigation, name 5 things you should collect information on?

1. Identifying information 2. Demographic information 3. Clinical information 4. Risk factor information 5. Source information

What are three sources of disease that need to be considered and/or controlled in a disease outbreak situation?

1. Infected animals 2. Feed/Bedding/manure/animal products etc 3. People

What are three types of bias?

1. Information bias 2. Selection bias 3. Confounding

What are three things that R0 determines that make it a useful parameter?

1. Likelihood that an outbreak will occur (>1 epidemic, <1 no epidemic) 2. The magnitude of the attack rate 3. The level of vaccination required to end an outbreak (aka level of herd immunity required to prevent a new outbreak)

What are the four assumptions for using a regression model?

1. Linearity (mean of Y is a linear function of X1, X2, etc) 2. Normality (each error is normally distributed) 3. Equal variance (all errors have same mean (0) and variance) 4. Independence (all errors are independent)

What are three advantages of a cross sectional study design?

1. Low cost 2. Quick 3. Can examine many different exposures

You need specific high-risk factors on a given premises to efficiently transmit Theileria equi (equine piroplasmosis) to other horses by tick borne transmission. Name four of those.

1. Multiple infected horses 2. Heavy infestation by competent tick vectors 3. Maintenance of competent vectors year round 4. Long periods of time in high-risk conditions

What are two limitations of a cross-sectional study design?

1. No time sequence between exposure and outcome 2. Cannot measure incidence

To establish a causal relationship between a parasite and a disease, what are the four Henle-Koch Postulates that must be fufilled?

1. Organism found in all animals suffering from disease, but not in healthy animals 2. Organism must be isolated from a diseased animal and grown in pure culture 3. Cultured organism should cause disease when introduced into healthy animals 4. Organism must be re-isolated from experimentally infected animals

What are four minimum data requirements for active surveillance?

1. Population at risk (herds/animals and their location) 2. Exits from population (# routinely slaughtered, dead from unknown causes, exported, other) 3. Slaughter plant/rendering plant locations 4. Disposal of animals that die from unknown causes

Surveys in cross sectional studies are used for what three purposes?

1. Prevalence of the disease/health event 2. Frequency of risk factors 3. Relationship of risk factors and disease

What are three goals when responding to a highly contagious disease ?

1. Preventing contact between susceptible animals and the disease agent 2. Stopping or limiting the production of disease agent by infected animals 3. Increasing the disease resistance of susceptible animals

What are six examples of information bias?

1. Questionnaire faults 2. Interviewer bias 3. Bias from surrogate interviews (i.e. parent) 4. Respondent errors 5. Bias from abstracting records 6. Misclassification bias

What are two good thing about cross sectional studies?

1. Quick/easy 2. Include a comparison group

What are five ways to control for confounding?

1. Randomization 2. Restriction 3. Matching 4. Stratification 5. Multivariate analysis

What are 3 advantages of a case control study design?

1. Rare diseases 2. Less cost and time 3. Can look at many different exposures

What are three ways to reduce R0?

1. Reduce susceptibility of uninfected individuals (i.e. vaccination) 2. Reduce infectiousness of infected individuals (i.e. through treatment or isolation) 3. Reduce contact rates in population (i.e. social distancing)

Name at least three useful aspects regarding a case series study

1. Report rare complications that are not documented elsewhere 2. New and emerging disease may first be documented here 3. Serve as early indicators of novel developments 4. Hypothesis generating 5. Help refine diagnostic criteria

What are at least three things seen in animals affected with Brucella canis ?

1. Reproductive failure (late term abortion, early embryonic death) 2. Discospondylitis, lymphadentitis, epididymitis, orchitis, prostatits 3. Incubation period is variable 4. many dogs are subclinical or asymptomatic 5. Chronic infections possible 6. Shedding can be intermittent and low #s

In an outbreak investigation, the first or second step is often to verify the diagnosis/confirm the outbreak. How can you confirm the diagnosis (4)?

1. Review laboratory results and methods 2. Interview farm managers 3. consult subject matter experts 4. Consider other reasons for increased reports (reporting procedures, case definitions, disease awareness increased, changes in diagnostic testing, population size/composition)

When is the use of sentinel animals appropriate in a disease outbreak?

1. Species used is very disease susceptible 2. Easier than monitoring the target population (may be unable to test target population or vaccine usage suppresses ability to detect in target population)

In confidence intervals, the margin of error depends on what three things?

1. Standard deviation of sample data 2. Sample size 3. Confidence (typically 95%)

Give 3 examples of lab tests/specimen samples to analyze in the event of a foodborne illness outbreak

1. Stool specimens from patients (standard enterics such as Salmonella, shigella, campylobacter, e. coli, yersinia and viruses such as norovirus) 2. Test food specimens 3. compare PFGE analysis (DNA fingerprinting) of patient and food specimens

What are the three steps in a cohort study?

1. Take a representative sample from the population and divide them into two groups according to exposure 2. Wait - maybe years! 3. Count the number with the outcome of interest

What are the nine guidelines for assessing causality?

1. Temporal relationship 2. Strength of association 3. Dose response relationship 4. Replication of findings 5. Biological plausibility 6. Consideration of alternate explanations 7. Cessation of exposure 8. Consistency with other knowledge 9. Specificity of association

What are the 9 causal criteria to assess the likelihood that causal association exists (Sir Bradford Hills)?

1. Temporal sequence 2. Strength of association 3. Consistency of effect 4. Biological gradient 5. Specificity of association 6. Coherence with established facts 7. Biologic plausibility 8. Analogy 9. Experiment

You are testing to see if a treatment has a different effect on the mean weights of laboratory rats. You run an ANOVA and find a p-value of <0.001. What can you can you conclude regarding the weights of the rats?

1. The four conditions do NOT have the same effect on the weights 2. At least one condition differs from at least one other condition BUT - you only know they're different, not which ones specifically are different (i.e. don't know if group 3 differs from group 4)

Name at least four criteria that surveillance systems should meet to be recommended for public health systems

1. Useful (contribute to control) 2. Simple (easy to use/operate) 3. Flexible (ability to adapt to changing needs of end users) 4. Acceptable (willingness of participants to provide requested data) 5. Stable (system can collect/manage/provide data w/o failure) 6. Documented 7. Cost effective (cost per case detected) 8. Practical (realistic and appropriate given infrastructure) 9. Sensitive 10. Good positive predictive value 11. Timely (time between case detection and notification to USDA) 12. Representative (tested samples represent geographic distribution of population at risk)

What are three key features of a confounder?

1. Variable is associated with exposure of interest 2. Variable associated with outcome of interest 3. Variable is NOT in the causal pathway (not an intervening variable)

What are the first four steps of an outbreak investigation?

1. Verify the diagnosis/confirm the outbreak 2. Define a case and conduct case finding 3. Tabulate and orient data (person, place time) - descriptive epidemiology 4. Develop a hypothesis

What are two limitations of a case control study design?

1. cannot estimate rate or risk 2. Selection bias - occurs when controls are not representative of the population that produced the cases

What items should be considered for disposal in a disease outbreak situation (5)?

1. carcasses 2. waste (liquid and solid) 3. animal products (meat/milk/hides/etc) 4. Personal Protective Equipment (PPE) 5. Any item that may be contaminated and when disinfection is not possible or economical

What are the four assumptions when running an ANOVA?

1. each population is normally distributed 2. all populations have the same variance 3. all samples are random and independent 4. the error is normally distributed with a mean of 0

What are four things you can infer from an epidemic curve (the number of cases over time)?

1. estimate magnitude and time trend 2. determine exposure period 3. predict course of epidemic 4. suggest type of epidemic

Name at least three characteristics of the agent, Brucella canis

1. gram negative coccobacillus 2. worldwide distribution (except Australia/New Zealand) 3. Shed in birth products, vaginal discharge, milk, semen, urine (less in salivia, naso-ocular secretions, feces) 4. Transmission is via ingestion, genital/oronasal/conjunctival mucosa/close contact/in utero 5. May persist in animals post treatment 6. Zoonotic

What are three recommendations for preventing campylobacter in a veterinary clinic?

1. hand hygiene before and after each patient contact, especially with puppies (naive immune system) 2. When patients are known to be fed a raw food diet should be handled using barrier precautions and not allowed to hang out in the waiting room 3. Don't eat and drink where there are patients or have patients where you eat and rink

What are three problems with a case series study?

1. intervention described may not have influenced the outcome 2. description may be atypical of the disease 3. may be harm attached to the intervention that was not apparent in these cases

What are four ways Contagious Equine Metritis can be spread?

1. live cover breeding 2. fomites and inadequate biosecurity (shared AV, wash bucket, iatrogenic spread) 3. AI (can contaminate semen) 4. Transmission to foals possible in utero or during foaling

Name at least three potential environmental risk factors relating to the spread of highly pathogenic avian influenza virus for poultry farms

1. poultry density 2. distance to nearest body of water 3. density of corn (attracts migratory fowl) 4. distance to major highways 5. Proximity to other infected farms 6. Rainfall and temperature changes that are conducive to virus survival

What are two things a regression equation can be used for?

1. prediction (i.e. production medicine) 2. identify or quantify association (risk factors)

Equine herpesvirus 1 can present what 3 ways?

1. respiratory signs 2. neurological signs 3. abortion/neonatal death

What are the four conditions for a binomial distribution?

1. the number of trials is fixed 2. Two outcomes (i.e. each trial is either success or failure) 3. the probability of success is the same for all trials 4. the trials are independent

What are two characteristics that define a cohort study?

1. well defined groups of exposed and non-exposed individuals 2. track and compare disease or outcome among exposed and non-exposed

The first quartile is also known as the _____________ percentile

25th

What is the incubation period of Rabbit Hemorrhage Disease Virus 2 (RHDV2)?

3-9 days

What is the typical incubation period of Leptospirosis?

5-14 days

What is the incubation period of leptospirosis?

5-15 days in animals 2-10 days in people

What are the last four steps of an outbreak investigation?

5. Evaluate/ test hypothesis (reform if needed) 6. plan and execute additional studies 7. implement and evaluate control/prevention measures (as early as possible) 8. communicate findings

The second quartile is also known as the ___________ percentile or the __________

50th percentile or the median

The third quartile is also known as the ____________ percentile

75th percentile

What value of the correlation coefficient (r) represents a very good to excellent relationship?

>0.75

5. Match the following terms to their definitions: A. A causal factor that is neither necessary nor sufficient, but increases the likelihood of disease, all other things being equal. B. Any factor that must be present for the disease to occur. C. Any factor or, more commonly a constellation of factors, that inevitably lead to the disease i. Sufficient cause ii. Necessary cause iii. Contributing cause

A - iii B - ii C - i

What is a collider?

A common effect that distorts the association between exposure and outcome, caused by attempts to control for the this common effect of the exposure and outcome

A (confounder/collider) gives a distorted association when failing to control for it, while a (confounder/collider) gives a distorted association when it is controlled for

A confounder gives a distorted association when failing to control for it, while a collider gives a distorted association when it is controlled for

5. Match the following terms to their definitions: A. A causal factor that is neither necessary nor sufficient, but increases the likelihood of disease, all other things being equal. B. Any factor that must be present for the disease to occur. C. Any factor or, more commonly a constellation of factors, that inevitably lead to the disease. i. Sufficient cause ii. Necessary cause iii. Contributing cause

A. A causal factor that is neither necessary nor sufficient, but increases the likelihood of disease, all other things being equal. -iii. Contributing cause B. Any factor that must be present for the disease to occur. -ii. Necessary cause C. Any factor or, more commonly a constellation of factors, that inevitably lead to the disease. -i. Sufficient cause

10. A new treatment is developed that prevents death but does not produce recovery from disease. Which of the following will occur? A. Prevalence will increase B. Prevalence will decrease C. Incidence will increase D. Incidence will decrease E. None of the above

A. Prevalence will increase

A new treatment is developed that prevents death but does not produce recovery from disease. Which of the following will occur? A. Prevalence will increase B. Prevalence will decrease C. Incidence will increase D. Incidence will decrease E. None of the above

A. Prevalence will increase

9. In a study of alcohol and oral cancer the relative risk is 2.0 for men and 2.0 for women but 4.0 for both sexes combined. This suggests that: A. There is confounding by sex in these data B. There is confounding by some unknown or unmeasured factor in these data C. There is evidence of effect modification in these data D. The results have been adjusted for age and sex E. The results are due to bias

A. There is confounding by sex in these data

In a study of alcohol and oral cancer the relative risk is 2.0 for men and 2.0 for women but 4.0 for both sexes combined. This suggests that: A. There is confounding by sex in these data B. There is confounding by some unknown or unmeasured factor in these data C. There is evidence of effect modification in these data D. The results have been adjusted for age and sex E. The results are due to bias

A. There is confounding by sex in these data

If you are comparing the mean between more than two groups of parametric data, what test would you use?

ANOVA

If you have a several samples of means or medians and want to run a parametric test, what would you run?

ANOVA Linear Regression

What are the two types of data collection in surveillance?

Active and Passive

What are three examples of propagative transmission?

Aerosol transmission Fomites Sexually

How is equine herpesvirus 1 transmitted?

Aersol or formite

If we determine an association between an exposure an an outcome exists, which of the following is a possibility to explain the association? a. It's real b. Selection bias accounts for it c. Information bias accounts for it d. It's confounding the association between another risk factor and disease e. It's due to error in conducting the study f. It's due to chance g. All of the above h. A, B, C, E, F only

All of the above

__________________ is a process that prevents foreknowledge of treatment assignment and thus shields those who enroll participants from being influenced by this knowledge

Allocation concealment

What is the difference between allocation concealment and blinding?

Allocation concealment protects the assignment sequence (treatment) until allocation Blinding protects the sequence after allocation

Allocation concealment seeks to prevent _____________ bias while blinding seeks to prevent ________________ bias

Allocation concealment seeks to prevent selection bias while blinding seeks to prevent information (performance and ascertainment) bias

What value in statistical testing provides the % chance of incorrectly claiming that a significant association exists

Alpha i.e. alpha at 0.05 = 5% chance of incorrectly claiming a significant association exists between variables

In words, how do you describe test sensitivity?

Among disease positive animals, it is the proportion that are test postive

Describe, in words, negative predictive value

Among test negative animals, it is the proportion that are disease negative

Describe, in words, positive predictive value

Among test positive animals, it is the proportion that are disease positive

An area under the curve value of _______ denotes a useless test and __________ denotes a perfect test

An area under the curve value of 0.5 denotes a useless test and 1 denotes a perfect test

Collecting data on potential confounding variables while conducting the study, then stratifying it it, is what way of controlling for confounding?

Analysis

What are the two categories of observational studies?

Analytic or Descriptive

_____________ epidemiology compares groups with different characteristics, tests significant associations with risk factors or exposures, and searches for the causes of and factors contributing to disease

Analytical

What are the four criteria that a case definition should include?

Animal/Farm ("person") Place Time Diagnostic criteria

When stopping the spread of disease, what are four things that movement should be controlled of?

Animals/animal products People Feed Vehicles

In a dynamic population, when can you sample for controls during the study time?

Anytime!

___________________ is the most widely used index to summarize the accuracy of continous tests

Area under the curve (AUC)

What are four locations where horses can mix (and therefore important to think about in disease outbreaks)

Athletic events Training facilities Breeding facilities Veterinary hospitals

_____________ ________________ among the exposed estimates how much of the outcome can be attributed to the exposure it self

Attributable Risk

What risk calculation would be helpful to know to answer the question, how much of the risk (incidence) of disease can we hope to prevent if exposure in question is eliminated?

Attributable Risk ("background risk") (incidence in exposed minus incidence in non exposed)

The incidence in the population minus the incidence in the unexposed is the formula for.....

Attributable risk

An epidemiologic study tests the following hypothesis: There is no association between having a pet dog in the household and the occurrence of multiple sclerosis (ms) in a household resident. The study utilizes a case control procedure and the results are: Odds ratio = 2.62; 95% confidence interval = 0.9 - 5.26 The correct conclusion is: A. Reject the null hypothesis. B. Accept the null hypothesis. C. Accept the alternative hypothesis. D. The ms incidence rate in the exposed group is 2.62 times the ms incident rate in the nonexposed group. E. The study is statistically significant at the 5% level.

B. Accept the null hypothesis. (CI includes 1)

In the simple linear regression formula, ___________ equals the expected change in Y per unit increase in X

B1

What is the causative agent of equine piroplasmosis (2)?

Babesia caballi Theileria (Babesia) equi

The binomial distribution is derived from a process known as a ?

Bernoulli trial

What type of virus is Porcine Hemagglutinating Encephalomyelitis virus (PHEV)?

Betacoronavirus Enveloped, single stranded RNA

Any systematic error in the design, conduct, or analysis of a study that results in a mistaken estimate of an exposure's effect on risk of disease is known as ?

Bias

The _______________ distribution can be used to approximate the Poisson distribution when n is large (>/= 20) and p is small (</= 0.05)

Binomial -Mean=λ = np -Variance=λ= np(1-p)

What are the two distributions of discrete variables?

Binomial or Poisson

What are three known vectors of Vesicular Stomatitis Virus?

Black flies Sand flies Culicoides

Name a prodcut that can be used to disinfect items from Rabbit Hemorrhage Disease Virus 2 (RHDV2)

Bleach (5 min contact time) 1% Virkon S. (10 min contact time) Rescue/Hydrogen peroxide (5 min contact time)

What is the difference between blinding and double blinding?

Blinding is only preventing the patients from knowing which group they were assigned to Double blinding is preventing BOTH the patient and the investigator from knowing which group the patient was assigned

Give an example of population interactions of the host that may influence disease outcome/susceptibility/exposure

Both intrinsic and extrinsic host factors including immunity, age, gender, breed, use/occupation, diet, travel, behavior

What is the assumption that should be met if you are planning on using the Pearson method to get a correlation coefficient?

Both variables are normally distributed

For an etiologic factor to be judged to be causally related to a disease, which of the following must be true? A) the etiologic factor is equally distributed through the population B) The etiologic factor is found among all cases of the disease C) Exposure to the etiologic factor must precede the onset of the disease D) Persons exposed to the etiologic factor have a higher prevalence of disease E) The results of an epidemiologic study of the factor must be externally valid

C) Exposure to the etiologic factor must precede the onset of the disease

Experimental studies differ from observational studies in which of the following? A. They can test a hypothesis B. They can estimate a measure of effect (e.g. relative risk) C. The investigator assigns who is exposed D. They identify a priori what are the exposures and outcomes of interest

C. The investigator assigns who is exposed

What are four things about Campylobacter that can be classified into the agent part of the epidemiological triad?

Campylobacter jejuni/Campylobacter coli Gram negative, curved rod Shed in feces Transmission is via direct or indirect contact (fecal-oral), under cooked poultry/other meat Low infectious dose in humans

A ___________ is a subclinical animal/patient that is not necessary to perpetuate agent

Carrier (note difference between reservoir)

A ___________ study typically examines multiple exposures in relation to a disease. Subjects are defined as cases and controls, and exposure histories are compared.

Case control

A ___________ study initially classifies subjects based on of diseased and non diseased cases, then looks within each group to determine if a risk factor was present or not

Case control study

In a _____________ study, there is a known outcome status of individuals, and you match cases with controls free of outcome and compare exposures

Case control study

What type of study design starts with cases and classifies them according to exposure status

Case control study

The proportion of cases that die of the disease is known as the ?

Case fatality rate

What is the difference between a case report and case series?

Case report is < 10 subjects Case series is > 10 subjects

What is the weakest study type ?

Case report or case series

A ___________ ____________ is a study in which provides a description of the ways in which the same disease manifests itself in a group of animals. It indicates the frequency of particular clinical signs.

Case series

In a cross sectional study, because you measure everything all at the same time, what is one problem regarding inferences about exposure?

You don't really know if the exposure occurred BEFORE the outcome of interest or vice versa, so not great for demonstrating causation

What is a type II error?

You fail to reject H0, when in fact it is false

In a case control study, you measure the exposure after having found the cases and controls, so what is one problem about inference of the exposure of interest?

You have no idea if the exposure occurred before the outcome of interest or vice versa, so bad if trying to demonstrate causation

What is a type I error?

You reject H0, when in fact it is true

If you are testing your data for normality, and you get a p value of <0.05 what does this mean?

You reject the null which assumes the data is normally distributed, and therefore assume the data is nonparametric

If you were to convert a 2 x 2 incidence table to adjust for the background rate using the multiplicative model, how would you adjust each cell?

You would divide the incidence rate where both factors are negative in each cell

If you were to convert a 2 x 2 incidence table to adjust for the background rate using the additive model, how would you adjust each cell?

You would subtract the incidence of disease where both factors are negative from each cell

If you are comparing two population means, and the variance within them is known OR your sample size is large (both n>30), what test would you run?

Z test

If you are comparing two population proportions with large sample size and population, what test would you use?

Z test

What is the formula to express attributable risk as a proportion (% attributable risk)

[ incidence in exposed - incidence in non exposed ] / incidence in exposed

2. One of your clients has a feedlot containing 15,000 cattle, 10,000 of which are susceptible. In a current outbreak of disease, 3,000 became sick and 300 died. The case fatality rate was: a. 10% b. 25% c. 2% d. 30% e. 3%

a. 10%

One of your clients has a feedlot containing 15,000 cattle, 10,000 of which are susceptible. In a current outbreak of disease, 3,000 became sick and 300 died. The case fatality rate was a. 10% b. 25% c. 2% d. 30% e. 3%

a. 10%

10. A decrease in the prevalence of a disease could be interpreted as a result of: a. A reduction in the incidence. b. A more rapid cure. c. A shorter life span of affected individuals. d. "a" and "c" above. e. All of the above.

a. A reduction in the incidence. b. A more rapid cure. c. A shorter life span of affected individuals. d. "a" and "c" above. e. All of the above.

1. The specific morbidity rate is usually the number of: a. Cases of a specific disease per 1,000,000 population b. Deaths from a specific disease for a geographical area c. Cases of a specific disease for a political area d. Deaths from a specific disease per 100,000 population e. Deaths from a specific disease per 100 cases of that disease

a. Cases of a specific disease per 1,000,000 population

The specific morbidity rate is usually the number of: a. Cases of a specific disease per 1,000,000 population b. Deaths from a specific disease for a geographical area c. Cases of a specific disease for a political area d. Deaths from a specific disease per 100,000 population e. Deaths from a specific disease per 100 cases of that disease

a. Cases of a specific disease per 1,000,000 population

1. Which one of the following frustrations would you most likely expect in preparing to carry out cohort studies on animal disease? a. Costly and time consuming, and plagued by the continual changing of the cohort. b. Difficult time in selecting a comparison group or control population upon which to test your hypothesis. c. Cohort populations are unchanging, and that no new individuals are introduced into the study population. d. Data collected retrospectively is often incomplete, and plagued by high degrees of institutional bias. e. Unable to get accurate estimates of incidence or prevalence of the disease using the cohort study technique.

a. Costly and time consuming, and plagued by the continual changing of the cohort.

Which one of the following frustrations would you most likely expect in preparing to carry out cohort studies on animal disease? a. Costly and time consuming, and plagued by the continual changing of the cohort. b. Difficult time in selecting a comparison group or control population upon which to test your hypothesis. c. Cohort populations are unchanging, and that no new individuals are introduced into the study population. d. Data collected retrospectively is often incomplete, and plagued by high degrees of institutional bias. e. Unable to get accurate estimates of incidence or prevalence of the disease using the cohort study technique.

a. Costly and time consuming, and plagued by the continual changing of the cohort.

7. The occurrence in a community or region of cases of an illness in the human population clearly in excess of normal expectancy and derived from a common propagated source is an: a. Epidemic b. Endemic c. Pandemic d. Epizootic e. Anthropozoonosis

a. Epidemic

The occurrence in a community or region of cases of an illness in the human population clearly in excess of normal expectancy and derived from a common propagated source is an: a. Epidemic b. Endemic c. Pandemic d. Epizootic e. Anthropozoonosis

a. Epidemic

8. Which of the following agent characteristics is most likely to be seen in a disease which occurs in epidemic proportions: a. High infectivity b. High pathogenicity c. High virulence d. Low antigenicity e. Viability

a. High infectivity

Which of the following agent characteristics is most likely to be seen in a disease which occurs in epidemic proportions: a. High infectivity b. High pathogenicity c. High virulence d. Low antigenicity e. Viability

a. High infectivity

5. The duration of a chronic disease process may complicate the epidemiologic study of its prevalence because of: a. Loss of people or animals from the study by death from other causes b. Changes in diagnostic techniques during the period of study c. Changes in medical or veterinary care during the period of study d. Decrease in interest level on the part of workers in the study e. All of the above

a. Loss of people or animals from the study by death from other causes b. Changes in diagnostic techniques during the period of study c. Changes in medical or veterinary care during the period of study d. Decrease in interest level on the part of workers in the study e. All of the above

6. The measure most sensitive to extremes is: a. Mean b. Median c. Mode d. Sample e. Inferential

a. Mean

The measure most sensitive to extremes is: a. Mean b. Median c. Mode d. Sample e. Inferential

a. Mean

3. The amount of health disorder existing in a population at one particular time, regardless of time of onset is known at the: a. Prevalence b. Incidence c. Morbidity rate d. Mortality rate e. Attack rate

a. Prevalence

The amount of health disorder existing in a population at one particular time, regardless of time of onset is known at the: a. Prevalence b. Incidence c. Morbidity rate d. Mortality rate e. Attack rate

a. Prevalence

7. Generalizability is best assured by: a. Representative nature b. Randomness c. Sample size d. Precise manipulation e. Statistical validity

a. Representative nature

Generalizability is best assured by: a. Representative nature b. Randomness c. Sample size d. Precise manipulation e. Statistical validity

a. Representative nature

4. It has been suggested that physicians may examine women who use oral contraceptives more often or more thoroughly than women who do not. If so , and if an association is observed between phlebitis and oral contraceptive use, the association may be due to a. Surveillance bias b. Selection bias c. Interviewer bias d. Nonresponse bias e. Recall bias

a. Surveillance bias

You compared two means and obtained a p value equal to 0.03. What is the correct way to summarize this? a. There is a 3% chance of observing a difference as large as you observed even if the two population means are identical (null hypothesis is true) b. Random sampling from identical populations would lead to a difference smaller than you observed in 97% of experiments, and larger than you observed in 3% of experiments c. There is a 97% chance that the difference you observed reflects a real difference between populations, and a 3% chance the difference is due to chance d. all of the above e. a and b only f. none of the above

a. There is a 3% chance of observing a difference as large as you observed even if the two population means are identical (null hypothesis is true) b. Random sampling from identical populations would lead to a difference smaller than you observed in 97% of experiments, and larger than you observed in 3% of experiments e. a and b only

A study wishes to assess birth characteristics of dairy calves in a population. Which of the following variables describes the appropriate measurement scale or type? A. Continuous B. Ordinal C. Nominal D. Dichotomous a. ___ Birthweight in kilograms b. ____ Birthweight classified as low, medium, high c. _____ Dam classified as primiparous, multiparous d. ____ Delivery type classified as natural, assisted, cesarean

a. _A. Continous__ Birthweight in kilograms b. __B. Ordinal__ Birthweight classified as low, medium, high c. __D. Dichotomous___ Dam classified as primiparous, multiparous d. __C. Nominal __ Delivery type classified as natural, assisted, cesarean

Which of the following variables are categorical? a. age groups b. height c. gender d. obesity e. weight

a. age groups c. gender d. obesity

Which of the following does absolute risk do? a. indicate magnitude of risk in a group of people with a certain exposure b. take into consideration the risk of disease in non-exposed individuals c. indicate whether an exposure is associated with increased risk of disease d. all of the above

a. indicate magnitude of risk in a group of people with a certain exposure Note: absolute risk is defined as the incidence of disease in a population

How is Equine Herpesvirus 1 or 4 spread?

airborne/ respiratory route (direct contact)

What are standard values for alpha and beta in error testing?

alpha = 0.05 Beta = 0.2

In words, how do you describe test specificity

among disease negative animals, it is the proportion that are test negative

In an ANOVA, the ___________ measures the extent of differences between the estimated treatment level means around the overall mean

among sum of squares (SSA)

Charting cases of a disease overtime is also known as creating what?

an epidemic curve

Effect modification is also known as ?

an interaction

The occurrence of more cases of disease than expected is considered.....?

an outbreak

Meta-analyses is a a _____________ type of study design

analytical

The _________ rate is the proportion of hosts infected during an epidemic episode

attack rate

4. A certain causal factor is thought to be associated with an extremely rare disease. What study plan would yield the best data with limited financial and human resources? a. Prevalence study. b. Case-control study. c. Prevalence study. d. Morbidity study. e. Case evaluation study.

b. Case-control study.

A certain causal factor is thought to be associated with an extremely rare disease. What study plan would yield the best data with limited financial and human resources? a. Prevalence study. b. Case-control study. c. Prevalence study. d. Morbidity study. e. Case evaluation study.

b. Case-control study.

3. What study plan would be best to determine the effectiveness of a new vaccine in preventing disease in humans? a. Case-control study. b. Cohort study. c. Prevalence study. d. Morbidity study. e. Retrospective study.

b. Cohort study.

What study plan would be best to determine the effectiveness of a new vaccine in preventing disease in humans? a. Case-control study. b. Cohort study. c. Prevalence study. d. Morbidity study. e. Retrospective study.

b. Cohort study.

A sample is a. a set that contains all the information about everyone or everything b. data that is just one part of the entire set c. what advertisers give to consumers to get them to try a product d. a collection of variables

b. data that is just one part of the entire set

Which of the following variables are discrete? a. body weight b. monthly ER visits between 1 Jan 19 - 1 Jan 20 c. number of surgical procedures for dogs with torn CCL d. number of abnormal chest radiographs e. Systolic blood pressure f. waiting times for elective surgery g. temperatures

b. monthly ER visits between 1 Jan 19 - 1 Jan 20 c. number of surgical procedures for dogs with torn CCL d. number of abnormal chest radiographs

__________ is a type of distribution that has two possible outcomes

binomal

A large study of serum cholesterol levels in patients with diabetes mellitus reveals that the parameter is normally distributed with a mean of 230 mg/dL and standard deviation of 10 mg/dL. According to these results, 95% of serum cholesterol observations in these patients lie between which of the following limits? a. 220 and 240 mg/dL b. 225 and 235 mg/dL c. 210 and 250 mg/dL d. 200 and 260 mg/dL e. 220 and 260 mg/dL

c. 210 and 250 mg/dL

6. When an epidemiologist is called to investigate a communicable disease emergency, the first thing he/she should try to determine is: a. Possible sources of infection b. Methods of transmission c. Accuracy of the diagnosis d. Methods of control e. Extent of spread

c. Accuracy of the diagnosis

When an epidemiologist is called to investigate a communicable disease emergency, the first thing he/she should try to determine is: a. Possible sources of infection b. Methods of transmission c. Accuracy of the diagnosis d. Methods of control e. Extent of spread

c. Accuracy of the diagnosis

Which of the following studies can test a hypothesis? a. Case report b. Case series c. Cohort study d. All of the above

c. Cohort study Need a comparison group for the others to test; they are hypothesis generating only

Veterinarians at a veterinary clinic report an increased incidence of lymphoma in dogs seen at their clinic. They note that some households in the community are exposed to chemical waste from a nearby factory. They believe that chemical waste causes lymphoma. If a study is designed to evaluate this claim, which of the following subjects are most likely to comprise the control group? a. Dogs exposed to the chemical waste that do not suffer from lymphoma b. Dogs not exposed to the chemical waste who do not suffer from lymphoma c. Dogs from the clinic that do not suffer from lymphoma d. Dogs not exposed to the chemical waste that suffer from lymphoma e. Dogs that suffered from lymphoma but got cured

c. Dogs from the clinic that do not suffer from lymphoma

A right-skewed distribution has a. a bell-shape b. a tail that goes to the left c. a tail that goes to the right d. one mode

c. a tail that goes to the right

In general, screening should be undertaken for diseases with the following features: a. diseases with a low prevalence in identifiable subgroups of the population b. diseases for which case-fatality rates are low c. diseases with a natural history that can be altered by medical intervention d. diseases that are readily diagnosed and for which treatment efficacy has been shown to be equivocal in evidence from a number of clinical trials e. none of the above

c. diseases with a natural history that can be altered by medical intervention

1. In a large case-control study of patients with pancreatic cancer, 17% of the patients were found to be diabetic at the time of diagnosis, compared to 4% of a well-matched control group (matched by age, sex, ethnic group and several other characteristics) that was examined for diabetes at the same time as the cases were diagnosed. It was concluded that the diabetes played a causal role in the pancreatic cancer. This conclusion: a. is correct b. may be incorrect because there is no control or comparison group c. may be incorrect because of failure to establish the time sequence between onset of the diabetes and diagnosis of pancreatic cancer. d. may be incorrect because of less complete ascertainment of diabetes in the pancreatic cancer cases. e. may be incorrect because of more complete ascertainment of pancreatic cancer in nondiabetic persons.

c. may be incorrect because of failure to establish the time sequence between onset of the diabetes and diagnosis of pancreatic cancer.

What type of virus is Rabbit Hemorrhage Disease Virus 2 (RHDV2)?

calicvirus

Blood type is an example of a (categorical/numerical) variable

categorical

In general, what does it mean when there is a significant interaction between two predictor variables in a multi variable regression model?

combined effect of the two predictor variables differs from the sum of their individual effects

In a case control study, _____________ are used to estimate the exposure distribution in the population from which the cases arose

controls

A ______________ study looks at a population at risk and takes a representative sample, concurrently classifying them as disease positive or negative and risk factor positive or negative

cross sectional

A _______________ study typically examines relationship between exposure and disease prevalence in a defined population at a single point in time

cross sectional

Which of the following study designs can a relative risk or risk ratio NOT be used in? a. Cohort study b. Randomized control study c. Cross-sectional studies d. Case-control studies

d. Case-control studies This is because the probability of disease is determined by enrollment

.In prospective study or cohort type of epidemiologic study, two types of cohorts are selected. One of these is the exposed and the other is: a. Cases b. Susceptible c. Affected cohorts d. Non-exposed e. Immune populations

d. Non-exposed

4. In prospective study or cohort type of epidemiologic study, two types of cohorts are selected. One of these is the exposed and the other is: a. Cases b. Susceptible c. Affected cohorts d. Non-exposed e. Immune populations

d. Non-exposed

8. Which of the following is NOT associated with a retrospective study? a. Adaptable to conditions of low prevalence. b. Less expensive than prospective. c. Requires fewer personnel. d. Takes longer to conduct. e. Provides less accurate incidence rate.

d. Takes longer to conduct.

Which of the following is NOT associated with a retrospective study? a. Adaptable to conditions of low prevalence. b. Less expensive than prospective. c. Requires fewer personnel. d. Takes longer to conduct. e. Provides less accurate incidence rate.

d. Takes longer to conduct.

9. An epidemic curve displays: a. The population at risk versus the frequency of cases. b. The frequency of cases versus the number of ill in the population. c. The time of onset versus the population at risk. d. The time of onset versus the frequency of incident cases. e. The time of onset versus the number of individuals who are ill.

d. The time of onset versus the frequency of incident cases.

Discrete probability distributions can be a. graphs b. tables c. equations d. all of the above

d. all of the above

Which of the following would you NOT run a chi squared test for? a. Comparing the variances of two populations b. Comparing the frequencies observed in different dog breeds presenting to the ER over the course of year, to see if they are different c. test to see if the data you obtained fits a normal distribution d. compare the means between two populations to see if they are different e. none of the above (chi squared should be used for all examples)

d. compare the means between two populations to see if they are different (use a t test)

If the Pearson product moment (r) or population (p) correlation coefficient is close to -1, then Y (increases/decreases) as X increases

decreases

Calculation of frequencies and proportions is considered ____________ epidemiology

descriptive

What is the difference between an analytic study and descriptive study (both observational study types) ?

descriptive: describes what is going on in a given population analytical: uses observations to compare populations and test a hypothesis

What type of bias is a cohort study prone to?

diagnostic/non participation bias loss-to-follow up

What is the difference between a diagnostic test and a screening test?

diagnostic: applied to individuals for purpose of confirming or ruling out a diagnosis screening: applied to apparently healthy individuals to purpose of early diagnosis of disease

Unlike linear regression, survival analysis has a _______________________ outcome

dichotomous

In Logistic regression the outcome variable is ____________

dichotomous (most commonly presence or absence of disease or mortality; only two possible outcomes)

3. Which of the following is an approach to handling confounding? a. Individual matching b. Stratification c. Group matching d. Adjustment e. All of the above

e. All of the above

The duration of a chronic disease process may complicate the epidemiologic study of its prevalence because of: a. Loss of people or animals from the study by death from other causes b. Changes in diagnostic techniques during the period of study c. Changes in medical or veterinary care during the period of study d. Decrease in interest level on the part of workers in the study e. All of the above

e. All of the above

A decrease in the prevalence of a disease could be interpreted as a result of: a. A reduction in the incidence b. A more rapid cure. c. A shorter life span of affected individuals. d. "a" and "c" above. e. All of the above.

e. All of the above.

2. Ecologic fallacy refers to: a. Assessing exposure in large groups rather than in many small groups. b. Assessing outcome in large groups rather than in many small groups. c. Examining correlations of exposure and outcome rather than time trends. d. Failure to examine temporal relationships between exposure and outcomes. e. Ascribing the characteristics of a group to every individual in that group.

e. Ascribing the characteristics of a group to every individual in that group.

A study is conducted to assess the relationship between breed and end-stage renal disease in cats. Two groups of pathologists independently study specimens from 1,000 kidney biopsies. The first group of pathologists is aware of the breed of the patient from whom the biopsy came, while the second group is blinded as to the patient's breed. The first group reports 'hypertensive nephropathy' much more frequently for domestic shorthairs than the second group. Which of the following types of bias is most likely present in this study? a. Confounding b. Nonresponse bias c. Recall bias d. Referral bias e. Observer bias

e. Observer bias

Incorrectly attributing population characteristics to individuals is known as the?

ecologic fallacy

Influenza is an enveloped or non enveloped virus?

enveloped - easy to kill

_______________ is the genuine state of uncertainty whether treatment is beneficial

equipose

A _______________ study studies prevention and treatments for diseases; investigator actively manipulates which groups receive the agent under study

experimental

What does a relative risk of 0 mean?

exposure has no effect on outcome

An odds ratio of < 1 means what?

exposure is negatively associated

What does a risk ratio < 1 mean?

exposure is negatively associated with outcome or protective against outcome

What does a relative risk of >1 mean

exposure is positively associated with outcome

A cohort study is good for rare exposures or outcomes?

exposures

The "steps" on a Kaplan-Meier survival estimate curve occur at the ______________ times

failure times

To calculate the sensitivity and specificity of a test, we must know the truth in the population from another source, typically the ?

gold standard

What type of parasite causes equine piroplasmosis?

hemoparasites (Babesia or Theileria)

When is a Fishers Exact test used instead of a chi-squared test?

if expected frequencies are low (if 20% or more of the cells are less than 5)

_________________ is when a comparison group does not appropriately represent the population from which cases arose, and is a type of selection bias

inappropriate comparison group

R^2 will (increase/decrease) as more variables are added to a model

increase

As sample size (increases/decreases), the confidence interval becomes more narrow

increases

For a given alpha and magnitude of effect (RR or OR), beta can be reduced ONLY by what?

increasing sample size

What is the difference between the interval scale and the ratio scale in numerical data?

interval scale: Zero does NOT denote the absence of the attribute being measured (i.e. a temperature of zero is not "no temperature" Ratio scale: Zero denotes absence of attribute being measured (i.e. weight).

__________________ bias is when an interviewer interjects his or her bias into the interview

interviewer

There is an _____________ association between sensitivity and specificity

inverse (trade one for the other)

A (high/low) prevalence of disease results in a low predictive value

low prevalence

For data that is symmetrically distributed the __________ is typically the preferred measure of central tendency because it is a better representative of a typical observation and it takes into account all values

mean

The ____________ is a good estimate of a typical value for non-symmetric (skewed) distributions

median

The first quartile or 25th percentile is calculated how?

median of the lower half of the observations

_________ regression has more than one predictor variable

multivariable

If a confidence interval has (wide/narrow) range, you are more certain of the value

narrow

(Parametric/Nonparametric) distributions are asymmetrical or skewed

nonparametric

(Parametric/Nonparametric) distributions are summarized or reported by the median (range)

nonparametric

Survival times are usually (parametric/nonparametric)

nonparametric

The ________ suggests no association between the predictor variable and outcome of interest

null hypothesis (H0)

BMI is an example of a (categorical/numerical) variable

numerical

What is the standardized mortality ratio formula?

observed deaths / expected deaths

In a case control study, exposure distribution in cases is compared to the exposure distribution in controls to compute _____________ as a measure of association

odds ratio

If you have one sample of proportions, what test would you run?

one sample z-test

What is the formula for the proportion of animals in a herd that would need to be vaccinated to establish herd immunity?

p = (1 - (1/R0) )

A ____________ is the probability under a specified statistical model that a statistical summary of the data (e.g. the sample mean difference between two compared groups) would be equal to or more extreme than its observed value

p value

The __________ for a hypothesis test is the probability of obtaining, when H0 is true, a value of the test statistic as extreme as or more extreme (in the direction supporting Ha) than one actually computed

p value

If you are comparing the mean between a single group with paired parametric data, what test would you use?

paired t-test

If you have a sample of means or medians that are matched pairs, and want to run a parametric test, what test would you do?

paired t-test

When testing in (series/parallel), animals that test positive to one test, the other test, or both tests are considered positive

parallel

(Parametric/Nonparametric) distributions are summarized or reported by the mean and standard deviation

parametric

Highly specific tests increase the _____________ and increase our confidence that a test positive subject is affected

positive predictive value

In an outbreak investigation, an animal with epidemiological information consistent with the disease AND a positive screening test would be considered a ____________ case

presumptive positive (needs confirmation by definitive testing)

_____________ prevention is conducted during the susceptibility stage of disease

primary

How do you calculate relative survival?

probability of survival with factor or condition / probability of survival without a factor or condition i.e. 5 year survival of individuals >75 w/colon cancer = 35.8%; prob of survival w/o cancer = 61% Relative survival = 0.358/0.61 = 0.587

The number of deaths from a specified disease in a specified time period in a specified location divided by the total deaths in a specified time period in a specified location is known as .... ?

proportionate mortality

What is the definition of an infected zone of control?

quarantined area around the infected or presumed infected premises

_______________ error is variability in the data that can not be readily explained

random error

In the formula Y = β0 + β1X1 + ...+ βkXk + ε, what does β1 represent if it is a continuous predictor?

represents the amount that the log odds of disease change with a unit increase in the predictor

What is the definition of surveillance or movement control zone ?

restricted area around the infected zone

A Pap smear at an annual well-woman checkup in a patient with previously normal Pap smears is an example of _______________ prevention

secondary

___________ prevention is intended to reduce duration and severity of disease

secondary

____________ prevention is conducted during the sub clinical phase of disease

secondary

A test that is more (sensitive/specific) is better for ruling out a disease

sensitive

The ____________ of a test is the likelihood of a positive test among those with the disease

sensitivity

When testing in (series/parallel), only animals that test positive to both tests are considered test positive

series

____________ ____________ sampling is when every unit observation has equal probability (same chance) to be selected into a sample

simple random sampling

A test that is more (sensitive/specific) is better for ruling in a disease

specific

The higher the ___________________ of the test, the higher the predictive value

specificity

____________ is ongoing observations with a plan of action based on the outcome

surveillance

In an outbreak investigation, any animal with clinical signs consistent with the disease, or history of exposure, or an inconclusive positive test would be considered a ___________ case

suspect

If you used an F test which found that the variables in your multiple regression model DO contribute significantly to the prediction of Y (dependent variable), how would you determine which specific variables are significant?

t Test

If you are comparing two population means, and the variance within them is NOT known AND your sample size is small (both n<30), what test would you run?

t test

The _________ test is a parametric test that looks for the differences between means of independent samples

t test

If you are comparing the mean between two independent groups of parametric data, what test would you use?

t-test

If you have one sample of means or medians, and you want to run a parametric test, what would it be?

t-test

What is the diagnostic sensitivity?

the PROBABILITY that the test correctly identifies an infected animal

In the formula Y = β0 + β1X1 + ...+ βkXk + ε, what does β1 represent if it is a dichotomous predictor?

the amount that the log odds of disease change when the factor is present

The association between the exposure and outcome of interest in a case control study is measured by ?

the odds ratio

What is the diagnostic specificity?

the probability that the test correctly identifies an uninfected animal

What does the p value represent?

the probability that the test statistic would be as large or larger than calculated if the null hypothesis were true Standard rejection of null occurs at small p-value, usually <0.05

Unlike logistic regression, survival analysis analyzes _________________

the time to an event

Where is equine piroplasmosis endemic?

tropical and subtropical areas of Mexico, central and South America, Africa, Asia, the Middle East, Europe and the Carribbean (but NOT the US)

what is the formula for negative predictive value ?

true negatives / all test negative d/(c+d)

If you have two samples of means or medians, and you want to run a parametric test, what would it be?

two sample t-test

__________ regression has only one predictor variable

univariable

Where is Leptospira shed?

urine

How do you convert the coefficient or log odds to an odds ratio or relative risk?

using the e function (i.e. if the coefficient was 0.8, then e^0.8 = 2.2 = odds ratio)

In an ANOVA, the error mean square (MSE) is an estimate of?

variance

What type of environment does Leptospirosis thrive in?

warm, humid environments Susceptible to dry environments and common disinfectants

When is random error reduced to zero?

when the study becomes infinitely large

In an ANOVA test the ___________ measures the random variation of the observations around the respective estimated treatment level means

within sum of squares (SSW)

Name at least three equine specific disease that are OIE reportable

• African Horse Sickness • Contagious Equine Metritis • Dourine • Glanders • Equine Infectious Anemia • Equine Influenza • Equine Piroplasmosis • Equine Rhinopneumonitis • Equine Viral Arteritis • Western &Venezuelan Equine Encephalomyelitis

Name at least three criteria that would constitute a disease outbreak as being "high impact" or "high consequence"

• High morbidity or high mortality • Potential for human health implications • Foreign animal disease or domestic disease with new increased/unexpected virulence • Limited intervention options • Severe or debilitating trade ramifications • Outbreak that impacts a large number of equids/owners/premises • Any disease which elicits a palpable level of concern or panic in the equine industry

What is the difference between probability and odds?

• Probability of an event occurring is the fraction of times you expect to see that event in many trials. Range is 0 to 1. • Odds are defined as the probability that the event will occur divided by the probability that it will not occur. Range is zero to positive infinity.