What is a secondary attack rate?

Correct Answer: A

Rationale: Secondary attack rate (A) measures infection among contacts of a primary case (e.g., household spread). B, C, and D are broader or vague.

Correct Answer: B

Rationale: Descriptive studies (B) collect quantitative data (e.g., case counts) to describe patterns. A is qualitative, C is experimental, D is broad.

Correct Answer: B

Rationale: Observational studies (B) watch natural events (e.g., smoking-disease links). A and D are experimental, C is a byproduct.

Correct Answer: A

Rationale: Descriptive studies often collect qualitative data (A) to describe patterns (e.g., case reports), though quantitative (B) is also common. C and D are less typical.

Correct Answer: D

Rationale: Reverse causation bias (D) occurs when outcome affects perceived exposure (e.g., disease prompting recall). A is selection, B is broad, C is recall.