What is the Kaplan-Meier curve used for in epidemiology?

• A. To estimate survival probabilities over time, accounting for censoring.
• B. To measure average incidence rate in cohort.
• C. To assess prevalence in cross-sectional surveys.
• D. To plot the distribution of exposure.

Answer: (A)

Survival analysis focuses on time to an event, and the Kaplan-Meier curve provides a nonparametric estimate of the probability of surviving beyond each time point while handling censoring. It updates the survival probability only at observed event times; at each of those times, the conditional probability of surviving is (number at risk just before the time minus the number of events) divided by the number at risk. The overall curve is the product of these conditional probabilities, producing a step-like plot that declines as events occur and remains flat when there are gaps due to censoring. Censoring means some individuals are lost to follow-up or the study ends before the event happens, and they contribute to the risk set up to their censoring time but do not count as events, which is why the Kaplan-Meier method is appropriate for incomplete follow-up data. This approach is about estimating survival probabilities over time, not about incidence rates, prevalence in a cross-section, or the distribution of exposure.