Kaplan-Meier curves are used to what purpose in cohort studies?

• A. They estimate the survival function over time, show time-to-event data, and allow comparison of survival between groups via log-rank tests.
• B. They measure incidence rates per person-year.
• C. They provide hazard ratios without assumptions.
• D. They predict the exact time of event for each individual.

Answer: (A)

Kaplan-Meier curves estimate the survival function over time for time-to-event data, taking censoring into account. They show the probability of remaining event-free at successive time points and are especially useful in cohort studies for comparing groups because you can test whether their survival curves differ using the log-rank test.

They do not measure incidence rates per person-year, which require calculating events per unit of person-time rather than a survival probability. They also do not provide hazard ratios directly; that kind of estimate comes from modeling approaches like Cox regression that make assumptions about how hazards relate over time. And they do not predict the exact time of an event for an individual—rather, they give overall survival probabilities and illustrate how the risk evolves across the study period.