What information does a Kaplan-Meier curve provide in a cohort study, and what are its limitations?

• A. It shows time-to-event probability; limitations: doesn't adjust for covariates; assumes non-informative censoring
• B. It shows incidence rates per person-year; limitations: requires randomization
• C. It shows hazard ratios over time; limitations: unstable at long times
• D. It shows prevalence over time; limitations: cannot handle censoring

Answer: (A)

A Kaplan-Meier curve conveys time-to-event probability by estimating the survival function, the chance of remaining event-free up to each point in time. It is built from the observed event times and censored observations, so the curve steps down at each event and flattens when data are censored. This approach provides a clear, nonparametric view of how quickly events occur over time and supports comparison of groups by plotting separate curves.

The key limitations are that it does not adjust for covariates. It gives crude, unadjusted estimates of survival, so differences between groups could reflect factors other than the exposure or treatment of interest. To account for covariates, you’d use methods like the Cox model or stratified analyses. It also relies on the assumption of non-informative censoring: the reason a participant is censored is independent of their risk of the event. If censoring is related to prognosis, the estimated survival probabilities can be biased.