Epi Midterm
stratified sample
A pre-established (calculated) number of subjects are randomly selected from subsets of the total population (CNA).
quota sampling
A quota is established and subjects chosen until quota is met (65% male); often not representative
Absolute Risk Reduction (ARR)
ARR=CER-EER =(control event rate)-(experimental event rate) =(rate in untreated group)-(rate in treated group)
case-cohort studies
Similar to Nested Case-Control but controls are selected from the general cohort rather than matched to each case. -Advantage of this design is that since controls are not matched to each case, several diseases can be studied from same cohort
what is the difference between cohort and randomized clinical trial?
-the exposure in most cohort studies is potentially a toxic or carcinogenic substance -the exposure in most randomized trials is a treatment or preventative measure
Odds ratio
(axd)/(bxc) -case control can only use odds ratio, but cohort can use both odds ratio and relative risk
advantage of cross-sectional study
-Advantage of being able to simultaneously assess exposure and disease status (outcome) in a population ("assess" causality) -Relatively inexpensive and fairly good generalizability.
examples of surveys aka cross-sectional studies
-BRFSS - Behavioral Risk Factor Surveillance System -NHANES - National Health and Nutrition Survey -Most opinion and political polls.
limitations of case studies/case series studies
-Cannot be used to establish formal statistical association. -Since case report is often examination of single cases and therefore limits strong conclusion; case-series are often used.
Research into pizza consumption in various geographic regions revealed that a greater amount of pizza is consumed in college towns than non-college towns of the same population. Given this information can we assume that college student eat more pizza than their counterparts?
-Mostly agree -there could be an ecological fallacy -results of the study may not apply to individuals, countries, and regions
cross-sectional (prevalence study)
-Observes a population of interest at a single point in time or during a specific time interval ("snapshot"). -Can be used to survey or assess the health status of a population by gathering information from individuals such as history, habits, knowledge, and behavior
purpose of case studies/case series studies
-Often used to identify the beginning or presence of an epidemic or unusual outbreak. -Identify new diseases, complications, side-effects (anything new) -To formulate hypothesis for further study; suggest causality.
descriptive studies
-always observational -never experimental -researcher does not manipulate exposure -mainly concerned with person, place, and time -measure social, economic, and health conditions of a population such as birth and death information (ex: vital statistics)
three types of descriptive studies
-case study/case series study, -ecologic study (correlational study) -cross-sectional study (prevalence study)
what are the characteristics of randomized clinical trials?
-clear and specific hypothesis -carefully designed and rigidly enforced protocol -subjects randomly assigned to study groups -placebo or current treatment given to control groups (if used) -outcomes compared between treatment and control group or between treatment groups -participants followed over the same time period -more than one experimental intervention (exposure) can be examined at the same time
limitation of cross-sectional study
-difficult to determine when exposure occurred and therefore establish temporality needed to establish risk -Healthy Worker Effect -Preponderance of prevalent cases of long duration (subjects who have had condition for a long time and have "acclimated" e.g. coal miners)
advantages of simple randomization
-each treatment assignment is completely random -the number of patients on each treatment will not be radically different (maintain comparability) -easy to implement
ecologic studies aka correlational studies
-examine populations/groups -focus on the associations between exposures and outcomes in selected populations -data collected in the past/already exists
types of causal relationships
-factor is both necessary and sufficient (factor A alone is enough to cause disease) -factor is necessary, but not sufficient (factor A+B+C lead to disease-factor A needs to be present in conjunction with B&C to cause disease) -factor is sufficient but not necessary (A can cause disease but so can B&C so not necessary) -factor is neither necessary nor sufficient (most chronic diseases-multiple risk factors)-(factor A+B or factor C+D or factor E+F can cause disease so factor A is not necessary because C+D and E+F can cause the disease as well and it is not sufficient because it needs to be with factor B to cause the disease)
disadvantage of a quasi-experiment
-issue of internal validity because treatment and controls may not be comparable because of the lack of randomization -without randomization, the treatment and control groups cannot be assumed to be statistically equivalent unless the researcher can provide a "large sample size that reflects general population"
what are the characteristics of experimental study designs?
-most rigorous of the study designs -offers greatest control over the research environment -manipulates exposure for two or more groups of pepple
disadvantages of simple randomization
-possibility of uneven groups -time imbalance or chronological bias -not often used for experimental studies, used mostly for cross-sectional assessments and surveys
what does randomization produce in RCT?
-study groups are comparable with respect to known and unknown risk factors -study groups that remove investigator bias in the allocation of subjects
after which ratio do you start losing power for case-control matching?
1:4 (one case to four controls) Increasing the number of controls (same or different), increases the power of a study but only up a ratio of 1:4 (one case to four controls).
indirect cause
A causes B , but with intermediate effects
direct cause
A causes B without any intermediate effects
Incidence Density
All known cases that occurred in the total cohort during duration of study/ Person years of observation in total cohort per unit time -this is a RATE measure -average person-time incidence rate
advantage of ecologic studies
Advantage of being quick to perform and generating new hypothesis for exploration of risk factors.
Hospital control
Advantages: Easily identified and readily available; best to select from multiple hospitals; as likely to recall exposure as cases; more likely to cooperate than healthy subjects. Disadvantages: Not healthy; may have different selection process for admission; difficult to determine which diseases should be allowed (due to possible contributing factors).
Population-Based control
Advantages: Greatest comparability with cases; minimal potential for selection bias. Disadvantages: Costly; time consuming; more potential for recall bias; less motivated to participate.
Special groups control
Advantages: Healthy; cooperative; similar to cases on numerous factors. Disadvantages: Not representative of exposure in population.
Cumulative Incidence
All known cases that occurred in the baseline cohort/ Number of individuals enrolled at baseline -this is a RISK measure -measure of average risk
Special exposures cohort study
Atomic Bomb Casualty Commission (Japan), Dutch Family Survivors (effects of starvation), Sevesco (dioxin exposure)
case-control
Begins with subject who already have the disease (cases) and compares them to people who do not have the disease (controls)
retrospective cohort
Begins with subjects who have the outcome or potential for outcome, uses data collected in the past, and compares exposed to non-exposed subjects
national (CDC) sources of data
Behavior Risk Factor Surveillance System (BRFSS) National Health and Nutrition Examination Survey (NHANES) National Health Interview Survey (NHIS) Pregnancy Risk Assessment Monitoring System (PRAMS) United States Cancer Statistics Youth Risk Behavior Surveillance system (YRBSS) Other databases for dental health, fluoridation, etc.
Occupational (study of occupation) cohort study
Benzene Workers (Leukemia), Coke-Oven Workers (lung cancer), Asbestos Workers (lung cancer), Radium Dial Painters (oral cancer)
Occupational (convenience) cohort study
British Doctors Study (smoking), Nurses Study, London Civil Service (SES effect), Taiwanese Civil Servants (liver cancer)
case series aka clinical series
Can also be prospective or retrospective by tracking groups of patients with a known exposure and/or treatment into the future to examine records for exposure and outcome
what is the difference between case-control and retrospective cohort?
Case-Control Study begins with diseased and non-diseased subjects and Cohort Study begins with exposed and non-exposed subjects (no disease yet), even retrospectively.
group matching (or frequency matching)
Characteristics of controls are matched with same proportion as cases
confounding as an alternative explanation for possible causality
Could other variables have accounted for the perceived association? The observed relationship between the risk factor (independent variable) and the outcome (Dependent variable) is due to a third factor (another independent variable)
bias as an alternative explanation for possible causality
Could the observed association be occurring due to some sort of bias? Systemic error in the study design, data collection, or analysis that results in a mistaken association between the risk factor(s) and the outcome
chance as an alternative explanation for possible causality
Could the observed association be occurring simply by chance? Avoid this being the case by using statistical tests, proper sampling schemes, sample size, measures of association, significance and confidence intervals
example of retrospective cohort
Cowan Progesterone Deficiency and Breast Cancer Study Overall results not found to be significant (1.8 more risk 95% CI 0.88-4.0) but when stratified by pre-menopausal status, risk was significantly greater (5.4 higher risk, 95% CI 1.1- 4.9) -used old database but asked a new question or looked at a different exposure -Start with new exposure- exposure in terms of pre/post menopausal status not the original hormone replacement therapy
information bias
Different information collected for exposed as opposed to unexposed subjects; especially in retrospective studies ex: smoking, drinking, and drug usage-people are not honest with their status
disadvantage of ecologic studies
Disadvantage is that results for community/population may not infer to the individual.
simple random sample
Everyone in population has equal chance of being selected (community survey, census, etc.) -400 will give you 85% of reliability with all your results
individual matching (or matched pairs)
Each case is matched with one or more controls similar in terms of factors or variables of concern
purpose of cross-sectional study
Examines the relationship between diseases (or other events) and possible associated factors as they exist in the population at one point in time. Measures exposure prevalence to disease prevalence
randomized community trials
Experiment in which 1+ communities serve as the "subjects" instead of individuals -randomization occurs at the level of the community, subjects within the community are not randomly assigned
randomized clinical trials (RCT)
Experiment used to test efficacy of preventive or therapeutic interventions
local sources of data
Extrapolate from vital statistics Hospital records Surveys Community assessments
example of prospective cohort
Framingham Study Small town of 30,000 in Massachusetts (near Boston). Selected 5,127 men and women between 30 and 62 Studied Coronary Heart Disease (CHD) in the cohort over next 20+ years. Findings: CHD risk increases with age (more so among men then women), elevated blood pressure, cholesterol, smoking, obesity, diabetes, inactivity and habitual drinking
Cardiovascular disease cohort study
Framingham, Tecumseh, Evans County, Muscatine, Bogalusa
uses of descriptive studies
Generate hypotheses Monitor public health policy Conduct surveys Planning, assessment Guide further studies
attributable risk
How much of outcome is eliminated if you eliminate a certain exposure or risk
assessment bias
If researcher knows the purpose of study and exposures of interest, they may make spurious associations
ecological fallacy
Inaccurate inference from population or community results to the individual
recall bias
Intentionally or unintentionally, memory is not always reliable. -Among cases, since they are often much more sensitive to possible exposures, generally resulting in overestimate of risk. -Among controls, generally leading to underestimate of risk
Health Care Setting cohort study
National Collaborative Perinatal Project, Child Health and Development Studies (Kaiser), Patients treated with radiation (spondylitis)
Phase III of drug testing
Large scale randomized studies involving large samples; if drug passes this phase, it is approved for market -effect of drug, efficacy of drug i.e. how good does it work in the real world
case-crossover study
Mainly used to study causes of "acute" outcomes in situations where the suspected exposure is brief and only occur over a short time. Each case serves as their own (perfectly matched) control.
experiment
Manipulation of one or more independent variables to measure effect on dependent variable
Preventative Effect of Korean Ginseng for Acute Respiratory Illness: A Randomized and Double-Blind Clinical Trial Lee et. al "...A random number between 1 and 100 was generated by a computer for each subject. The randomization codes were hidden from all subjects, research staff, investigators and pharmacists until all the data were analyzed. The enrolled subjects were scheduled for the first visit, and subjects were randomly assigned to one of two groups, the concentrated red ginseng or placebo group. The prescription of the study products were 1.0g 3 times a day for 12 weeks. Placebos were made with the same taste and appearance but without the principal ingredients that present in the red ginseng extract..."
Masking was used in this RCT. a. true b. false c. more information is needed Looking at the article's title and the methodology, there is something wrong with the: a. type of blinding b. selection of participants c. the authors have an appropriate title what type of blinding was used in this RCT? a. single-blind design b. double-blind design c. triple-blind design those given study drug without the red ginseng (RG) extract are the: a. intervention group b. they all had drug with RG extract c. control group A, A, C, C
Veterans cohort study
Mustard Gas poisoning (WWI-lung disease), Vietnam Veterans (PTSD, Agent Orange), Gulf War Veterans (Gulf War Syndrome)
Number Needed to Harm (NNH)
NNH=1/ARR -number of patients needed to treat before you see one adverse event/side effect -rate of "side-effect" in the treated and non-treated groups -measure of risk in harming one person (NNH=1 means everyone hurt)
Number Needed to be Treated (NNT)
NNT=1/ARR NNT=1/CER-EER -number of people needed to treat in order to benefit one person/prevent one undesired outcome -rate of "experimental outcome" in treated and non-treated groups -ideal NNT=1 (everyone is cured in treated group; none in untreated)
Child Health cohort study
National Birthday Trust Studies (Midwife and birth outcome studies in England), Project on Premature Infants, National Children's Study
do friends make good controls?
No because you share too many characteristics with them
closed cohort
No subjects are added after the start of the study (although some cohorts may drop out or die before the end of the study). Investigators try to follow all cohort members to the end of the study -can measure either cumulative incidence or incidence density
Women in Switzerland; can we really say that fat intake for a specific individual is associated with breast cancer?
No; ecological fallacy -we know something is going but can't infer that it is fat b/c everything else says it's probably not the case
loss to follow-up bias
People with outcome often leave study and affect incidence rates
Famous Cohort Studies
Population-Based: -Cardiovascular Disease -Child Health -Special Exposures Non-Population Based: -Occupational (convenience) -Occupational (study of occupation) -Health Care Setting -Veterans
Phase IV of drug testing
Post-marketing surveillance studies to detect side effects that may not have been discernible during the previous phases or in the short-term -i.e. when companies tell you to contact a certain number if you experience a side effect after taking drug
case study
Qualitative description of a person, group (as one) or event. Researcher studies individual cases and seeks to explain causality.
analytic bias
Researchers and analysts may introduce their preconception into analysis and interpretation of findings
judgement sampling
Researchers choose subjects based on who they think would be most appropriate for the study; used when specific issue is being studied.
convenience or accidental sampling
Samples are chosen based on accessibility (friends, mall shoppers, etc.); prone to bias.
systemic sample
Subjects are selected based on some established scheme (every 5th person, every second house, LQAS, one school's 9th graders, etc.)
retrospective case study
Subjects are selected because historical records meet established criteria
case-control study
Subjects are selected on the basis of whether they have the disease (cases) or they don't have the disease (controls) starts with outcome-->exposure -best for RARE OUTCOME/DISEASE -can only calculate odds-ratio (a*d/b*c) -CANNOT estimate prevalence -good first step when exploring causal (etiology) relationship -less expensive alternative
prospective case study
Subjects included in study as they occur or are found meeting the criteria for inclusion
bias
Systematic error that results in incorrect estimate of the true effect of an exposure on the outcome of interest (a.k.a.: Error!) -introduces error and pervades entire study
publication bias (non-publication bias)
Tendency to only publish studies that have had positive results giving the wrong impression that all the studies find positive results
risk difference
The arithmetic difference between two cumulative incidences incidence of exposed-incidence of unexposed in terms of total
rate difference
The arithmetic difference between two incidence densities incidence of exposed-incidence of unexposed in terms of person time
triple-blind design
neither the subject or the researcher is aware of group assignment and the person administering the treatment (often a pharmacist) is blinded to what is actually being given
requisites for a risk factor
The frequency of the disease varies with the degree of exposure (could be how long [duration] or how often [frequency]). The risk factor must precede the disease. The observed association must not be due to any other source (bias or confounding).
Relative Risk or Risk Ratio
The ratio of two cumulative incidences incidence rate in exposed/incidence rate in unexposed (a/a+b)/(c/c+d) -cohort uses relative risk -calculate in closed cohort
open cohort
The study takes on new members and may lose members as the study progresses. Also called a Dynamic Cohort or Dynamic Population -can only measure incidence density
state sources of data
Vital records, birth defects monitoring, cancer registry, cardiovascular disease and stroke, chronic illnesses, diabetes, environmental illnesses, HIV/STD/AIDS, infectious disease, injury and trauma, mental health, substance abuse, tuberculosis, vaccine preventable diseases and zoonotic diseases.
non-consecutive
only select participants included in the results
cause
a condition or characteristic that precedes the outcome event and without which the outcome event would not have occurred at all or would not have occurred until sometime later
cohort
a population group, or subset thereof, that is followed over a period of time; group with some sort of specific commonality
case definition
a statement that specifically describes the characteristics a subject must have to be considered a "case."
Factor A, B, or C can each individually cause a certain disease without the other two factors, but only when followed by exposure to factor X. Exposure to factor X alone is not followed by the disease, but the disease never occurs in the absence of exposure to factor X. Factor X is:
a. A necessary and sufficient cause b. A necessary, but not sufficient cause c. A sufficient, but not necessary cause d. Neither necessary nor sufficient B
analytic epidemiology
concerned with hypotheses and the association between exposures and outcomes and the strength of this association
types of case series studies
consecutive or non-consecutive
survey is an example of what type of study?
cross-sectional study
controls
do not have the disease
double-blind design
neither subject nor researcher is aware of group assignment
A study assessed the impact of sun exposure on skin damage in beach volleyball players. During a weekend tournament, players from one team were asked to wear waterproof, SPF 35 sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball tournament players' skin from both teams was analyzed for texture, sun damage, and burns. Comparisons of skin damage were then made based on the use of sunscreen. This is an example of ________
a) Prospective Cohort b) Retrospective Cohort c) Case-Control d) Experimental D
The power of a study with a 20% chance of type II error is:
a. 20% b. 80% c. 100% d. None of the above B
Which of the following is a cross sectional study?
a. A study describing the prevalence of depression among adult patients with Rheumatoid Arthritis in a hospital survey. b. A study describing prevalence of developmental disorders among children with Autism when mother breastfed through infancy. c. A study describing the prevalence of elevated blood pressure among incarcerated perpetrators of domestic abuse. d. A study describing the prevalence of a history of drug abuse in relation to the long-term compliance with a diet program. A.
Which of the following is a cross-sectional study?
a. A study describing the prevalence of smoking among high school students in Harris county. b. To determine the association between smoking and lung cancer, a researcher compared the smoking histories of 500 subjects with lung cancer and 1000 subjects without lung cancer. c. Two groups of elderly subjects - one group vaccinated, the other group unvaccinated were studied to determine the long-term effectiveness of influenza vaccines in elderly people. d. To determine if a history of abuse was associated with crime, past records were reviewed to establish a correlation. A.
The probability of observing a difference when a difference exists:
a. Alpha b. Beta c. Power d. None of the above C
A study describing the 5 cases of West Nile Virus disease in Tarrant County in 2012 is an example of _____
a. Case series b. Case-control c. Cross-sectional d. Ecological Study A.
A researcher set out to investigate the relationship between three major allergic diseases, asthma, allergic rhinitis (AR), and atopic dermatitis (AD), and psychological and behavioral problems in preschoolers. He conducted a survey using a modified International Study of Asthma and Allergies in Childhood questionnaire to determine the prevalence of symptoms and diagnosed allergic diseases, and a Korean version of the Child Behavior Checklist to assess internalizing, externalizing, and sleep problems among 780 preschoolers. This is a ____study design.
a. Case series b. Case-control c. Cross-sectional d. Ecological Study C.
A study comparing the prevalence of cardiovascular disease in the US with the prevalence of cardiovascular disease in Japan is an example of _____
a. Case series b. Case-control c. Cross-sectional d. Ecological Study D.
To study the association between knowledge and behaviors related to HIV in high school students, a questionnaire to assess knowledge about prevalence, causes and individual susceptibility to HIV and practice of risky sexual behaviors was administered. This is an example of which type of study?
a. Case series b. Case-control c. Cross-sectional d. None of the above C.
What study design can incorporate consecutive and non consecutive participants?
a. Case series b. Ecological c. Cross-sectional d. Nested Case-series A.
Which of the following is not a method of simple randomization?
a. Choosing a group with a particular exposure b. Tossing a coin for allocation to one of two groups c. Using a random digit table d. Using a computer generated randomized number program A
Which of the following is not a descriptive study?
a. Cross-sectional b. Case series c. Ecological d. Experiment or Case-control D.
HIV super-infection (reinfection) has been reported in several settings, but no study has been designed and powered to rigorously compare its incidence to that of initial infection. Determining whether HIV infection reduces the risk of super-infection is critical to understanding whether an immune response to natural HIV infection is protective. This study compares the incidence of initial infection and super-infection in a group of high-risk women in Mombasa, Kenya. What is the study design?
a. Cross-sectional b. Cohort c. Randomized clinical trial d. Ecological B What is/are the key word/s that might define this study as a cohort study? a. Reinfection b. Risk c. Protective d. Incidence e. Both b and d E
A study conducted in 40 US clinical centers beginning in 1993. Enrolled were 10,739 postmenopausal women, aged 50-79 years, with prior hysterectomy, including 23% of minority race/ethnicity. Women were randomly assigned to receive either 0.625 mg/d of conjugated equine estrogen (CEE) or placebo. what is the study design?
a. Cross-sectional b. Cohort c. Randomized clinical trial d. Ecological C
We are conducting a study of obese vs non-obese subjects to see if they develop diabetes over time; subjects can be enrolled at any time during the course of the study. Therefore we can only measure.
a. Cumulative Incidence b. Incidence Density c. Incidence Difference d. Risk Difference B
An essential characteristic of cohort study is a comparison of outcomes in ________ and _________ groups.
a. Dead/Alive b. Diseased/Non-diseased c. Exposed/Unexposed d. Older/Younger C
What is the main difference between Descriptive and Analytic studies?
a. Descriptive studies only examine individuals b. Descriptive studies are experimental c. Descriptive studies do not manipulate exposure d. None of the above C.
A study that examines the death rates from colon cancer in each of the 50 U.S states in relation to the average percentage of residents in each state undergoing colonoscopy screening. This is an example of :
a. Ecologic b. Cross sectional c. Case control d. Cohort A.
Does the international variation in mean intake of salt among populations of middle-aged men correlate with the prevalence of hypertension? This is an example of a(n) ________ study.
a. Ecological b. Randomized Control Trial c. Experimental d. Cross Sectional A
A study that examines the death rates from cervical cancer in each of the 50 US states in relation to the average percentage of women in each state undergoing annual PAP smear screening. This is an example of ________
a. Ecological b. Retrospective Cohort c. Experimental d. Cross Sectional A
A study compared the prevalence of back pain among current members of the plumbers and pipe fitters union with that of current members of the bakers and confectionary union. This is an example of ________
a. Ecological b. Retrospective Cohort c. Experimental d. Cross Sectional D
Which of the following is not an experimental type of study?
a. Experiments b. Randomized control trials c. Randomized community trials d. Cross sectional study D
A study conducted in 40 US clinical centers beginning in 1993. Enrolled were 10,739 postmenopausal women, aged 50-79 years, with prior hysterectomy, including 23% of minority race/ethnicity. Women were randomly assigned to receive either 0.625 mg/d of conjugated equine estrogen (CEE) or placebo. why is this not a cohort study?
a. Exposure status is assigned b. Variables are not manipulated c. Exposure status is not assigned A
What is/are the advantage(s) of a cross-sectional study?
a. Good generalizability b. Expensive c. Can infer causality d. Can infer temporality A.
The type of error incurred when the study indicates there is a difference between treatment and control when in fact there is no difference is Type _________ error
a. I b. II c. I or II d. I and II both A
A study on gastric cancer is conducted using population data from various major cities across Japan. The researchers find a relationship between salt and gastric cancer in males. They conclude that Japanese men have a higher risk of developing gastric cancer if they consume salt. This inference is:
a. Inaccurate inference from population or community results to the individual. b. Inaccurate inference from the study population to the general population. c. Inaccurate inference from one study population to another study population d. Accurate inference A.
A researcher wants to make sure that the likelihood of his treatment and control groups are statistically equivalent and that the effects of confounding are minimalized. Which of the following is the best option:
a. Increase sample size b. Use matched pairs c. Conduct a robust cohort study d. Use randomization D
Prospective Cohort studies are more likely than Case-Control studies to have problems with:
a. Information Bias b. Recall Bias c. Loss to follow up d. Selection bias C
What is/are the limitation(s) of a cross-sectional study?
a. It only measures incidence b. The Healthy-Worker effect c. Preponderance of prevalent cases of long duration d. Both B and C D.
A study that is conducted on two different populations will probably not be generalizable because it:
a. Lacks internal validity b. Lacks external validity c. Will have poor predictive value d. Cannot determine the number necessary to treat B
Which of the following factors is not considered to estimate the sample size needed for a study?
a. Normality of the sample population b. Level of statistical significance (α) c. The value of the power desired (β) d. Whether the test should be one sided or two sided A
A pharmaceutical company has developed a new drug which was just approved for the market by FDA. This drug just completed which phase of testing?
a. Phase I b. Phase II c. Phase III d. Phase IV C
______ is used by not letting subjects know whether they are in treatment group or control group. It ensures _______
a. Placebo, consistency b. Masking, consistency c. Placebo, competency d. Masking, competency B
A study assessed the impact of sun exposure on skin damage in beach volleyball players. During a weekend tournament, players from one team were asked to wear waterproof, SPF 35 sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball tournament players' skin from both teams was analyzed for texture, sun damage, and burns. Comparisons of skin damage were then made based on the use of sunscreen. This is an example of ________
a. Prospective Cohort b. Experiment c. Case Control d. Cross Sectional B
A study assessed the impact of sun exposure on skin damage in beach volleyball players. During a weekend tournament, players from one team wore waterproof, SPF 35 sunscreen, while players from the other team did not wear any sunscreen. At the end of the volleyball tournament players' skin from both teams was analyzed for texture, sun damage, and burns. Comparisons of skin damage were then made based on the use of sunscreen. This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional A
To determine the long-term effectiveness of influenza vaccines in elderly people, cohorts of vaccinated elderly and unvaccinated community-dwelling elderly were studied over time. The results suggest that the elderly who are vaccinated have a reduced risk of hospitalization for pneumonia or influenza. . This is an example of a:
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional A
Vietnamese Experience Study: Subjects were several thousand soldiers stationed in Vietnam from 1969-1971 and several thousand soldiers stationed in Europe from 1969-1971. In the mid 1980s investigators, determined and compared the death rate and prevalence of illness in both groups. This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional B
A study evaluated the relationship between breast cancer and a woman's history of breastfeeding. The investigator selects women with breast cancer and an age-matched sample of women who live in the same neighborhoods as the women with breast cancer. Study subjects are interviewed to determine if they breastfed any of their children. This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional C
Subjects were persons with laboratory-confirmed trichinosis and one healthy friend of each. All subjects were asked about their consumption of pork and other meat products. This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional C
A researcher used data collected from high school students from Baltimore, Maryland, and studies the differences in tobacco use between a cohort of adolescents that worked for pay and a cohort of adolescents that did not work for pay. The results suggest that adolescents who work for pay have a higher risk of using tobacco. This is an example of a ________ study.
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional D
To determine the long-term effectiveness of influenza vaccines in elderly people, cohorts of vaccinated elderly and unvaccinated community-dwelling elderly were studied over a period of three years. The results suggest that the elderly who are vaccinated have a reduced risk of hospitalization for pneumonia or influenza.
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional A
A study examined the relationship between exposure to chest irradiation and subsequent risk of breast cancer that was begun in 2005. In this study, women who received radiation therapy for postpartum mastitis (an inflammation of the breast that occurs after giving birth) in the 1940s were compared to women who received a non-radiation therapy for postpartum mastitis in the 1940s. In this prior study, the women were followed for 50-60 years to determine the incidence rates of breast cancer in each group. This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Case Control d. Cross Sectional B
Subjects were children enrolled in a health maintenance organization (HMO). At 18 months of age, each child was randomly given one of two types of vaccines against Haemophilus influenzae. Parents were asked to record any side effects on a card, and mail it back after 2 weeks. This is an example of a ________
a. Prospective Cohort b. Retrospective Cohort c. Experiment d. Cross Sectional C
When reviewing a registry, do persons with colon cancer have a history of less physical activity in the 10 years preceding their diagnosis compared with other persons? This is an example of ________
a. Prospective Cohort b. Retrospective Cohort c. Experimental d. Cross Sectional B
To determine if a traffic light needs to be installed at a busy intersection, you would want to conduct what sort of study to establish driving patterns?
a. Prospective Cohort b. Retrospective Cohort c. Experimental d. Cross Sectional D
John Snow's investigation of the cholera outbreak in London is an example of a:
a. Quasi-Experiment b. Randomized Community Trial c. Case-Control Study d. Randomized Clinical Trial A
Temporal relation is easier to establish in _________ study.
a. Randomized Control Trial b. Cross Sectional c. Case Control d. Prospective Cohort D
A school based educational program was conducted to see if it influenced adolescents to adopt more active lifestyles. A total of sixteen schools across several states were randomly assigned to intervention and control groups. The students in both sets of schools filled out questionnaires and were weighed before and after the program. These schools were then compared to see if the intervention brought about any improvement in the activity levels (and weight) among adolescents. What is the study design?
a. Randomized clinical trial b. Cross-Sectional c. Randomized community trial d. Ecological C Why? Because exposure status is randomly assigned to each school
Non-probability samples are best used for:
a. Rare events b. Complex studies c. Population-based studies d. Both A and B D.
Cohort studies are best used for ________ whereas, case control studies are best used for _________.
a. Rare outcome, rare exposure b. Rare exposure, rare outcome c. Rare outcome, rare disease d. Rare disease, frequent exposure B
Confounding or bias are more common in __________.
a. Retrospective studies b. Prospective studies c. Cohort studies d. Case-control studies A
A researcher is comparing the two cancer drugs. He enrolls 1000 study subjects and randomly divides them into the two groups. One group will receive drug A and other will receive drug B over the course of next 3 months. However, neither the study subjects nor researcher is aware of the drug allocation. This kind of study design is
a. Single blind design b. Double blind design c. Triple blind design d. None of the above B
What are the 2 types of cohorts?
a. Static/Dynamic b. Open/Closed c. Forward/Backward d. Person/Animal B
A study examining the effects of a nearby waste disposal site sampled every fifth house in a series of neighborhoods. This is an example of what type of sampling?
a. Systemic sampling b. Stratified sampling c. Simple random sampling d. Quota sampling A.
What are case-studies/case series studies MOST often used for?
a. To detect an outbreak b. To determine causality c. To examine the burden of disease in a population d. To establish formal statistical association A.
Randomized clinical trials are usually used to test efficacy of preventive and therapeutic interventions
a. True b. False A
A study describing the prevalence of childhood obesity in Fort Worth is a Cross-Sectional study.
a. True b. False A.
Which of the following is not a characteristic of Randomized Controlled Trial?
a. Very clear and specific hypothesis b. Subjects are selectively assigned to study groups c. Participants in both group are followed over same time period d. Placebo or current treatment given to the control group B
what are the requirements for the cohort populations?
all members of the cohort population must: -be free of the disease at the start of the study -be at risk of developing the disease -must not be immune -must not be in non-susceptible group -must not be dead
variable
any attribute, phenomenon, event, time period, or object effect that can have different values, which research attempts to either quantify or control to examine the effect on the event of interest
risk factor
any exposure associated with a disease
prospective cohort (a.k.a. Concurrent Cohort or Longitudinal Study)
begins with Exposure, identifies exposures as they occur and follow subjects to determine if disease occurs and then compare incidence
Retrospective Cohort Design (a.k.a.: Historical or Non-Concurrent Prospective Study
begins with Outcome, and observes past history for exposure and compares incidence -different from retrospective case-control because in case-control only odds-ratios can be calculated, not incidence
analytical studies
can establish more of a causal link because they research risk and protective factors of diseases -often used to test hypotheses generated by descriptive studies
limitations to descriptive studies
cannot be used to test for the presence of valid statistical association (cannot infer causality); can only describe distribution of variables
A man using Methylene Chloride without respiratory protection to strip paint off an old bathtub in an unventilated room was found dead. CDC recommends using respiratory protection and good ventilation when using MC. The cause of death was presumed to be due to MC poisoning. Difficult to make sweeping generalization (although MC poisoning was indeed the case). case report or case series?
case report -only requires one person
Among 108 snowmobile drivers who died in snowmobile crashes in Ottawa, Canada, during 1985 through 1990, 79 (73%) had alcohol in their blood and 71 (65%) were intoxicated by Ottawa's legal standard.21 We regard this as strong evidence that alcohol use is associated with snowmobile crashes, since it seems unlikely that any reasonable selection of control snowmobile drivers would find that two thirds were legally intoxicated. case report or case series?
case series -series of events
which studies are subject to confounding by selection bias which limits inference on causality?
case study and case series studies
Phase II of drug testing
clinical investigations involving 100 to 200 subject to test efficacy and relative safety -strict lab conditions; see the efficacy of drug or intervention; efficacy is the clinical impact that a medication has
synergistic relationship
combined effect of two or more factors is greater than the sum of their individual effects
antagonistic relationship
combined effect of two or more factors is less than the sum of their individual effects; lessens relationship/effect between individual effects
matching
ensures cases and controls have similar observable characteristics; this will enable comparison of exposure/outcome between the 2 study groups by eliminating extraneous effect
probability sample
everyone in the population has a "non-zero" chance of being included (in other words, everyone has a chance of being included!)
observational analytical study
exposure status is NOT assigned Ex: cross-sectional study, cohort study, case-control study
experimental analytical study
exposure status is assigned Ex: experiments, randomized clinical trials, randomized community trials
external validity
generalizability; the extent to which a study can be inferred to the general population
benefit of NNT and NNH
helps make clinical decisions in research because you can see how benefit outweighs risk and vice versa
effectiveness
how well the agent/intervention does in "real-life" ***same equation as efficacy Effectiveness=(placebo rate)-(treatment rate)/ placebo rate
equivalence trials
hypothesis is that the two treatments are indistinguishable from each other -different drugs work the same
non-inferiority trials
hypothesis that new treatment is no worse than another -cheaper, less side-effect, easier to take
superiority trials
hypothesis that one treatment is better than another
descriptive epidemiology
identifies populations at higher risk for health problems by exploring prevalence and incidence in terms of person, place and time
Quasi (Natural) Experiment
in studies exploring harmful diseases, it is unethical to randomly expose subjects, so experimenters use observation via cohort or case-control studies; use existing exposures, compare to unexposed and determine if there is an increased risk; the investigator lacks full control over the allocation and/or timing of intervention but nonetheless conducts the study as if it were an experiment and allocating subjects to groups
stratified randomization
individuals are grouped into strata and then randomized to one treatment group -results in comparable groups
placebo
used to simulate that the actual treatment is given to ensure that controls will not 'imagine' the effects. Thereby, making the groups as comparable as possible
cases
people afflicted with a disease; usually confirmed on the basis of clinical signs or laboratory test (confirmed diagnosis).
non-probability sample
picking and choosing people in your study; best for complex or rare events
independent variable
predictor, controlled, manipulated, explanatory or exposure variable or risk factor -unaffected by other variables -affected by confounding variables
what are the sampling schemes for cross-sectional studies?
probability and non-probability sample
randomization
process by which each participant has the same/equal chance of being assigned to either the intervention or control group
internal validity
proper study methods; free from bias, sampling or systematic error
types of case studies
prospective or retrospective
efficacy
reduction of risk expressed as the rate of disease in the treatment group compared to the control group; measures how well the agent/intervention work under "ideal conditions" Efficacy=(placebo rate)-(treatment rate)/ placebo rate
dependent variable
response, experimental, outcome or measured variable -affected by the action or interaction of the independent variables
consecutive
results include all members of the study
Phase I of drug testing
small studies of 20-80 subjects to explore possible toxic effects -making sure you're not killing people; very controlled environment
cohort study
study of a population that is, has been or may be exposed to factors that are hypothesized to contribute towards the occurrence of a specific disease or other outcome; exposure not assigned (if exposure assigned-->experimental study) starts with exposure-->outcome -best for RARE EXPOSURE -can calculate relative risk (incidence) and odds-ratio -includes temporality
single-blind design
subject unaware of group assignment
rate ratio
the ratio of two incidence densities -calculate in open cohort (use person-time because people come and go)
Hill's criteria
there are 9 points and they are arguable; historical framework for establishing cause and effect relationship
what is the purpose of following a cohort?
to measure the occurrence of one or more specific diseases/outcomes during the follow-up period, usually with the aim of comparing the resulting rates between two or more cohorts
what do sources of data and data collection depend on?
type of study
masking (or blinding)
used by not letting subjects know whether they are in the treatment group or the control group
cross-sectional study
used in certain situations to determine exposure and outcome at the same time (simultaneously) -called prevalence study because no idea of temporality -can compare either prevalence of disease or prevalence of exposure
Healthy Worker Effect
workers seem to have lower morbidity/mortality rates because left work due to disability or death and therefore not included in study
