MPH Epidemiology & Biostatistics 2 — Questions and Answers
Question 1: In a case-control study, which measure of association is typically calculated?
- Relative risk
- Attributable risk
- Odds ratio (Correct answer)
- Incidence rate ratio
Correct answer: Odds ratio
Odds ratios are used in case-control studies because true incidence rates cannot be directly calculated from this design.
Question 2: What is 'selection bias' in epidemiological research?
- Misclassification of exposure or outcome
- Systematic error in how participants are recruited into a study (Correct answer)
- Confounding by an unmeasured variable
- Random error due to small sample size
Correct answer: Systematic error in how participants are recruited into a study
Selection bias occurs when study participants are systematically different from the target population due to flawed selection procedures.
Question 3: The number needed to treat (NNT) is the reciprocal of:
- Relative risk
- Odds ratio
- Absolute risk reduction (Correct answer)
- Number needed to harm
Correct answer: Absolute risk reduction
NNT = 1 / Absolute Risk Reduction, representing how many patients must be treated to prevent one additional adverse outcome.
Question 4: Which statistical test is appropriate for comparing means between two independent groups?
- Chi-square test
- Paired t-test
- Independent samples t-test (Correct answer)
- ANOVA
Correct answer: Independent samples t-test
The independent samples t-test compares means from two unrelated groups to determine if they differ significantly.
Question 5: Confounding in epidemiology refers to:
- Random error that distorts results
- A third variable that is associated with both exposure and outcome (Correct answer)
- Measurement error in the outcome variable
- Publication bias in the literature
Correct answer: A third variable that is associated with both exposure and outcome
A confounder is a variable related to both the exposure and the outcome that can distort the true association between them.
Question 6: What is the purpose of stratified analysis in epidemiology?
- To increase sample size
- To examine associations within subgroups and control for confounding (Correct answer)
- To randomize participants into groups
- To calculate incidence rates from prevalence data
Correct answer: To examine associations within subgroups and control for confounding
Stratified analysis divides data into subgroups to evaluate whether a third variable modifies or confounds the exposure-outcome relationship.
MPH Epidemiology & Biostatistics 2
In a case-control study, which measure of association is typically calculated?