What is a hazard ratio and in which study design is it commonly used?

• A. The ratio of hazard rates (instantaneous risk) over time; commonly used in survival analysis from cohort studies or RCTs
• B. The ratio of cumulative incidences over time; used in cohort studies
• C. The ratio of risk at study end; used in cross-sectional studies
• D. The ratio of prevalence; used in case-control studies

Answer: (A)