MCCQE Population Health and Epidemiology 2 — Questions and Answers
Question 1: A study follows 1,000 smokers and 1,000 non-smokers for 10 years to compare lung cancer incidence. What type of study is this?
- Case-control study
- Prospective cohort study (Correct answer)
- Cross-sectional study
- Randomized controlled trial
Correct answer: Prospective cohort study
A prospective cohort study follows groups with different exposures forward in time to measure disease incidence.
Question 2: In a screening program, the positive predictive value of a test is most influenced by which of the following?
- Test sensitivity
- Test specificity
- Prevalence of the disease in the screened population (Correct answer)
- Sample size of the study
Correct answer: Prevalence of the disease in the screened population
Positive predictive value depends heavily on disease prevalence; a highly specific test still has low PPV in low-prevalence populations.
Question 3: Which measure of disease frequency accounts for the time each individual is at risk?
- Cumulative incidence
- Incidence rate (person-time) (Correct answer)
- Point prevalence
- Period prevalence
Correct answer: Incidence rate (person-time)
Incidence rate (incidence density) uses person-time denominators to account for variable follow-up periods.
Question 4: A public health intervention reduces the relative risk of stroke from 0.40 to 0.20. What is the relative risk reduction?
- 20%
- 50% (Correct answer)
- 80%
- 60%
Correct answer: 50%
Relative risk reduction = (RR_old − RR_new) / RR_old = (0.40 − 0.20) / 0.40 = 50%.
Question 5: Herd immunity thresholds are primarily determined by which parameter?
- Case fatality rate
- Basic reproduction number (R₀) (Correct answer)
- Incubation period
- Secondary attack rate
Correct answer: Basic reproduction number (R₀)
The herd immunity threshold is calculated as 1 − 1/R₀; a higher R₀ requires greater population immunity.
Question 6: When comparing two interventions, which statistical measure directly quantifies the clinical importance of a treatment effect rather than just statistical significance?
- p-value
- 95% confidence interval width
- Effect size (e.g., Cohen's d) (Correct answer)
- Chi-square statistic
Correct answer: Effect size (e.g., Cohen's d)
Effect size measures the magnitude of the treatment difference, independent of sample size and statistical significance.
Question 7: A factory worker cohort has higher lung disease rates than the general population. Comparing to the general population introduces which bias?
- Recall bias
- Hawthorne effect
- Healthy worker effect (Correct answer)
- Berkson bias
Correct answer: Healthy worker effect
The healthy worker effect occurs because employed populations are generally healthier than the general population, underestimating occupational risks.
MCCQE Population Health and Epidemiology 2
A study follows 1,000 smokers and 1,000 non-smokers for 10 years to compare lung cancer incidence.
What type of study is this?