What is the purpose of an epidemiological study?

Correct Answer: B

Rationale: Epidemiology studies disease distribution and determinants (B) to inform public health. Vaccine development (A), treatment (C), and training (D) are not its primary aims.

Correct Answer: C

Rationale: Population at risk (C) is those susceptible (e.g., unvaccinated for measles). A is cases, B is immune, D is recovered.

Correct Answer: C

Rationale: Matching (C) controls confounders (e.g., age, sex) in case-control studies. A, B, and D are unrelated or incorrect.

Correct Answer: B

Rationale: Analytical studies (B) test hypotheses (e.g., does smoking cause cancer?). A is descriptive, C is hypothesis generation, D is clinical.

Correct Answer: B

Rationale: Cohort studies (B) select based on exposure (e.g., smokers vs. non-smokers). A is case-control, C and D are variables, not criteria.