Which type of bias occurs when the selection of participants into a study is related to both the exposure and the outcome?

Correct Answer: A

Rationale: Selection bias (A) occurs when entry relates to exposure and outcome (e.g., hospital-based controls). B is data error, C is recall, D is confounding.

Correct Answer: B

Rationale: Likelihood ratio > 1 (B) means a positive result favors disease (e.g., LR+ = sensitivity / (1-specificity)). A, C, and D misinterpret.

Correct Answer: C

Rationale: Tertiary prevention (C) reduces disease impact (e.g., rehab post-stroke). A is primary, B is secondary, D is specific.

Correct Answer: B

Rationale: Prevalence (B) quantifies disease burden (e.g., resource needs). A, C, and D are other aims.

Correct Answer: C

Rationale: Confounding (C) mixes effects (e.g., age in smoking-cancer). A is error, B is bias, D is modification.