Which of the following is a measure of disease frequency?

Correct Answer: A

Rationale: Incidence rate (A) measures new cases over time. B, C, and D are test performance metrics, not frequency.

Correct Answer: C

Rationale: Cohort studies (C) compare exposed vs. unexposed groups for outcomes (e.g., cancer rates). A is snapshot, B is retrospective, D is experimental.

Correct Answer: A

Rationale: Case reports (A) describe individual cases (e.g., new disease). B, C, and D are analytical or experimental.

Correct Answer: C

Rationale: Case-control studies use odds ratio (C) to measure association. A and D are cohort measures, B is cross-sectional.

Correct Answer: C

Rationale: A confounder (C) links exposure and outcome (e.g., age in smoking-cancer). A is the exposure, B is the outcome, D is bias.