Epidemiology Final
Risk Ratio Rquation
(A/n1)/(C/n2)
What are the properties of a cofounder?
- Must be an independent cause or predictor of the outcome (associated with outcome) - Must NOT be an intermediate step on the causal pathway (can NOT be an effect of the exposure.) - Must be an independent cause or predictor of the outcome (associated with outcome)
what are the key factors of information bias?
- always happens after participants are enrolled - differences in the way that information is collection - most common type (placed in wrong group) - comes from self reports, medical record errors, data entry errors, non-specific disease/exposure definitions
4 Components of an Outbreak
1. clinical (symptoms, lab results) 2. person (who gets the disease) 3. place (where is the disease happening) 4. time (what time period)
Properties of a confounder
1. must be an independent cause or predictor of the outcome 2. must be associated with the exposure 3. must NOT be an intermediate on the casual pathway
what causes a virus to spillover from animals to humans?
1. person must be exposed to animals 2. virus must be capable of infection humans
A person was enrolled in a study on the association between alcohol use and death on 1/1/2019. They were followed until 1/1/2020, at which point they were lost to follow up. On 1/1/2021 they turned up alive and resumed participating in the study until the study concluded on 1/1/2022. How many years of Person Time did this person contribute to the study?
3
What slice of the pie is the Necessary Cause?
A - it is present in every causal pie
Dynamic Populations
A population whose membership is defined by being in a state or condition
Fixed populations
A population whose membership is defined on the basis of some EVENT
Cumulative incidence equation
A/N where A = # of people developing disease during a specified time period and N = # of people followed for the specified time period
Incidence Rate equation
A/PT where A = new cases during time period and PT = total person - time of observation in a population at risk
The epidemiological triangle consists of:
Agent, host, disease
What are common control measures used in a disease outbreak?
Behavioral interventions Vaccine campaigns Medication distribution Person protective equipment
If we don't know the cause or pathogen of a disease, we can
Design and conduct an epidemiological study
What are the five components of an outbreak investigation?
Determine the cause (hypothesis) Design a study Collect and record data Control measures Communication
True or False: Poor recall is a type of recall bias
False
A student was exposed to SARS-CoV-2 on September 12. Their symptoms began on September 18. What do you call the time period between exposure and onset of syptoms?
Incubation period
The process of gaining the agreement of all eligible and willing individuals to participate in an experimental trial is referred to as which of the following?
Informed consent
Non-differential misclassification
Misclassification on one measure (exposure OR outcome) is independent of the other Can bias results toward or away from the null
differential misclassification
Misclassification on one measure (exposure OR outcome) is related to the other
What type of misclassification is this: When misclassification on one measure (exposure OR outcome) is independent of the other
Non-differential
What is the primary weakness of case control studies?
Not good for rare exposures
What is the primary weakness of cohort studies?
Not good for rare outcomes
What is the primary weakness of cross sectional studies?
Not good for rare outcomes or exposures
Prevalence equation
P/N where P = cases and N = population
What are the types of epidemiological surveillance
Passive, active, sentinel, syndromic, other (social media)
During an outbreak investigation we use surveillance to help us determine what characteristics of a disease?
Person, place, time
What do you need to know to measure disease frequency?
Population, time, and cases of the disease
Benefits of case counts
Provide an estimate of the magnitude and relative magnitude of the problem They are easy(-ier) to understand Useful in advocacy/public policy Useful for planning health care delivery
What is the main measure of infectivity?
R0
Infectivity
R0 = the basic reproductive number, the number of cases of average an infected person will cause during their infectious period
risk difference equation
Risk Difference (RD) = Riskexposed - Riskunexposed RD = (A/n1)-(C/n2)
Measures of association
Risk difference Risk ratio Incidence rate difference Incidence rate ratio Odds ratio Attributable risk
Relative Risk (RR)
Riskexposed/ Riskunexposed
Risk difference
The difference in risk of disease between the exposed and unexposed groups
Incidence
The occurrence of new cases of a disease in a population during a specified time period Involves the transition from one state to another Denominator only includes the population AT RISK
Cumulative Incidence
The proportion of a population at risk that develops the disease over a specified time period
Incubation
Time interval between initial contact with an infectious agent and appearance of the first sign or symptom of the disease in question
A study where subjects at risk of the outcome are defined according to their exposure and followed over time to determine the incidence of the outcome is called...
a cohort study
what type of measure is a risk ratio?
a relative measure
Prospective Cohort Study
a source population is divided into exposed and unexposed groups at the beginning of a study by researchers and their disease status is observed
Association
a statistical relationship between two variables
epidemic
a sudden increase in the number of cases, above what is normally expected
Outbreak
a true increase of disease above baseline
Odds Ratio Equation
ad/bc
odd ratio equation
ad/bc
what type of measure is a risk difference?
an absolute measure
What is the primary strength of a case control study?
an be conducted after exposures and cases have started
pandemic
an epidemic that spreads over several countries
endemic
baseline amount of a disease to is usually present in a community
What are the types of control measures?
behavioral, vaccination, medication, environmental measures, infection control, health education
Response Bias
bias that occurs due to the differences in people who are willing to participate in studies and those who don't. maximize response rates to minimize effects all study designs
measures of frequency
case counts, prevalence, risk/cumulative incidence, and incidence rate
The outcome is known at the beginning of what kind of study?
case-control study
Clusters
cases that are grouped in a time or space bu may not represent a real increase over time
The "lifetime risk of breast cancer" among women is a commonly cited measure of which of the following? prevalence, incidence rate, cumulative incidence, case counts
cumulative incidence
Interviewer Bias
difference in the way the information is solicited, recorded, or interpreted type of information bias
Absolute measures of association are some sort of __________ , while relative measures of association are some kind of __________
difference, ratio
How can we slow dug resistance?
do not share antibiotics/drugs poor hygiene avoid close contact with people who are ill keep vaccination up to date
An investigator identifies a strong association between ice cream and shark attacks. This association is likely:
due to confounding
period prevalence
during a time period
What slices of the pie are considered Component Causes?
each slice is a component cause
What is the primary strength of a cross sectional study?
easy and inexpensive
What were the main findings of the Dutch famine of 1944-1945?
effects of undernutrition were dependent of the timing of the onset of the famine
Cross-Sectional Study
examines the relationship between disease and other factors in a defined population at a single point - snapshot in time - measures exposures prevalence in relation to disease prevalence
Prevalence
existing disease burden
What type of experiment is considered the gold standard in epidemiology?
experimental
True or False: confounders are only associated with the exposure
false
True or False: the speed of drug resistance is uncontrollable
false
True or False? When the direction of the bias is toward the null, it means that the error causes the true measure of association to be overestimated.
false
What type of population depends on the the occurrence of an event?
fixed population
Systematic Error
flaws in design/conduct of a study that lead to an erroneous association between exposure and disease (consistently wrong in a particular direction)
What is the primary strength of a cohort study?
good for rare exposures
Inappropriate Control Selection
happens when the control group is not selected from the same population as the diseased/exposed group only happens in case-control studies
Information Bias
happens when the information you collect from/about your participants is erroneous
The ______ period is the time between initial contact with an infectious agent and the appearance of symptoms; the ______ period is the time between exposure and the onset of the infectious period (when you can transmit the disease).
incubation, latency
Case-Control Study
individuals from a source population are selected and divided into cases of disease and controls which are then compared
Bias that can occur if the data you collect from (or about) your participants is erroneous is called
information bias
What type of bias occurs AFTER participants are enrolled in the study
information bias
Incubation Period
interval between initial infection and first signs and symptoms
Fixed Population
membership is based on a event, it is permanent
Dynamic Population
membership is based on a state/condition, transient membership
How can we expedite drug resistance?
misusing antibiotics poor infection prevention/control measures living and working in unclean conditions mishandling food
Confounding
mixing of effects between an exposure, an outcome, and a third extraneous variable
Which of the following is a general word that can apply to a disease, condition, or event? Morbidity, mortality, incidence, and prevalence
morbidity
point prevalence equation
number of people w/ a disease at a time/the total population at that time
period prevalence equation
number of persons who have the disease during a specified time period / number of persons in the population during that specified period
Cumulative incidence
occurrence of a new disease
Selection Bias
one relevant group in the population has a higher probability of being selected
who accrues person time?
people at risk and while being followed
Which of the following refers to the proportion of the population that is diseased during a specified duration of time, such as the year 2021? point prevalence, period prevalence, and incidence rate
period prevalence
Components of a Case Definition
person, place, time
When a spike in disease cases serves as the source for future disease spikes, we see what kind of an outbreak curve?
propagated outbreak curve
Random Error
proportion of variation in a measurement that has no apparent connection to a measurement or variable (by chance)
An investigator sought to study the association between air pollution and COVID-19 on UVM's campus. The investigator enrolls 100 freshmen, gives them each an air monitor to monitor their air pollution, and follows them until graduation to see if they develop COVID. What kind of study design is this?
prospective cohort study
Case counts
raw numbers of disease
Selecting a diseased control group is the most common method for minimizing which type of bias?
recall bias
Retrospective Cohort Study
records are obtained of diseased and undisposed individuals from a source population and their exposure status is observed through records (in the past)
Bias due to differences in those who do and who do not agree to participate in a study due to both exposure and disease is called
response bias
An investigator is interested in the association between Tylenol use and Myocardial Infarction (a heart attack). The investigator has access to the Nurses Health Study data and pulls data reported by 3,000 women in 1981 and assess their reported Tylenol use. Then, the investigator evaluates whether any of these women developed a Myocardial Infarction before 2015. What kind of study design is this?
retrospective cohort study
What can we estimate in cohort studies?
risk difference, risk ratio, incidence rate, and cumulative incidence
What type of bias can occur when one group in the study population has a higher probability of being included in the study sample?
selection bias
point prevalence
specific point in time
Incidence rate
speed of new cases of disease
Case Definition
standard criteria for classifying whether a person has a particular disease
Association
statistical relationship between two variables
Person time
the amount of time an individual (or the population) is followed
What parts of the pie make up Sufficient Cause?
the complete pie
Causation
the exposure produces the effect
Causation
the exposure produces the risk
Infectivity
the number of cases on average an infected person will cause during their infectious period
latency period
the period between exposure and the onset of the period of communicability
odds ratio
the ratio for the odds of an event occurring in an exposed group to the odds of that event happening in the unexposed group specific for case control studies
risk ratio
the ratio of the probabilities of an event in the exposed vs unexposed groups
Latency Period
the time from exposure to infectiousness
True or False: drug resistance is naturally occurring
true
What factors have increased the number of infectious diseases?
urbanization, poverty, and climate change
Recall Bias
when cases and controls systematically have different memories of the past type of information bias
when does person time stop accruing?
when the person is no longer a part of the population at risk, they develop the disease, they die, is lost to follow-up, no longer meets the eligibility, observation period ends