Epidemiological measures of effect assess the between an exposure and an outcome.

Correct Answer: C

Rationale: Measures of effect (e.g., risk ratio, odds ratio) quantify the strength of the association between exposure and outcome (C), indicating how strongly they are linked (e.g., smoking and lung cancer). A is about causation, not measurement. B relates to intervention effects, not association strength. D addresses confounders, not the exposure-outcome link.

Correct Answer: C

Rationale: Herd immunity (C) is population resistance when a high proportion are immune (e.g., via vaccination, B), protecting others. A is individual, D is passive.

Correct Answer: B

Rationale: Case definition (B) standardizes criteria for consistent disease identification (e.g., COVID-19 symptoms/tests). A, C, and D are unrelated.

Correct Answer: C

Rationale: Cross-sectional studies (C) snapshot prevalence at one time (e.g., surveys). A is retrospective, B is longitudinal, D is experimental.

Correct Answer: B

Rationale: Cohort (prospective) follows exposure to outcome; case-control (retrospective) starts with outcome to exposure (B). A, C, and D aren’t primary differences.