Which of the following is a limitation of cross-sectional studies?

Correct Answer: C

Rationale: Cross-sectional studies (C) can’t determine causality due to simultaneous exposure-outcome measurement. A, B, and D may apply but aren’t primary.

Correct Answer: B

Rationale: Controls (B) in case-control studies lack the disease for comparison. A is cases, C and D confuse exposure status.

Correct Answer: B

Rationale: Selection bias occurs when participant selection distorts exposure-outcome relationships, but B (misclassification) is information bias. A (loss to follow-up) is attrition bias, often considered a form of selection bias in cohorts, yet the answer key lists B. C and D are recall and observer biases. The key may be incorrect; A aligns better with selection bias.

Correct Answer: C

Rationale: Matching (C) controls confounding in design (e.g., sex-matching). A is analysis, B is broad, D includes analysis methods.

Correct Answer: D

Rationale: Vulnerable populations need all (D): consent (A), rights protection (B), and safeguards (C) (e.g., children).