AMC MCQ Population Health and Epidemiology 2 — Questions and Answers
Question 1: A case-control study reports an odds ratio of 3.2 for smoking and a rare disease. What does this odds ratio best approximate?
- The relative risk of the disease (Correct answer)
- The absolute risk reduction
- The number needed to treat
- The attributable fraction in the population
Correct answer: The relative risk of the disease
For rare diseases the odds ratio closely approximates the relative risk because the disease odds approximate the disease risk.
Question 2: A new screening test has high sensitivity but low specificity. What is the most likely consequence in a low-prevalence population?
- Many false positives (Correct answer)
- Many false negatives
- High positive predictive value
- Low test recall
Correct answer: Many false positives
Low specificity combined with low disease prevalence generates a large number of false-positive results.
Question 3: Which measure quantifies the proportion of disease in exposed individuals attributable to the exposure?
- Attributable risk (risk difference) (Correct answer)
- Prevalence ratio
- Incidence density
- Standardised mortality ratio
Correct answer: Attributable risk (risk difference)
Attributable risk is the difference in risk between exposed and unexposed groups, reflecting excess risk due to exposure.
Question 4: In a randomised controlled trial, allocation concealment primarily protects against which bias?
- Selection bias (Correct answer)
- Recall bias
- Lead-time bias
- Detection bias from outcome assessors
Correct answer: Selection bias
Allocation concealment prevents foreknowledge of group assignment, reducing selection bias at enrolment.
Question 5: A study finds an association between coffee drinking and lung cancer, but smoking is more common among coffee drinkers. Smoking is best described as a:
- Confounder (Correct answer)
- Effect modifier
- Collider
- Mediator
Correct answer: Confounder
Smoking is associated with both the exposure and the outcome and is not on the causal pathway, making it a confounder.
Question 6: The basic reproduction number (R0) of a measles outbreak is 15. Approximately what herd immunity threshold is required to halt transmission?
- About 93% (Correct answer)
- About 50%
- About 15%
- About 75%
Correct answer: About 93%
The herd immunity threshold equals 1 minus 1/R0, which for R0 of 15 is roughly 93%.
Question 7: Which study design is most appropriate to estimate the prevalence of obesity in a community at a single point in time?
- Cross-sectional survey (Correct answer)
- Prospective cohort study
- Case-control study
- Randomised controlled trial
Correct answer: Cross-sectional survey
A cross-sectional survey measures exposure and outcome simultaneously, making it ideal for prevalence estimation.
AMC MCQ Population Health and Epidemiology 2
A case-control study reports an odds ratio of 3.2 for smoking and a rare disease.
What does this odds ratio best approximate?