Kaplan-Meier Survival Curve

A Kaplan-Meier survival curve is a stepwise graph that estimates the probability of survival over time. The curve begins at a survival probability of 1.0 and drops by a step at each event, while tick marks show censored subjects, so readers can see how survival declines across the follow-up period.

A Kaplan-Meier curve is stepwise because the estimated survival probability only changes at the exact times events occur and stays flat in between. Each downward step marks an event, which is why the curve looks like a descending staircase rather than a smooth, continuous line.

The small tick marks on a KM survival curve indicate censored observations — subjects who were lost to follow-up or had not experienced the event when the study ended. Censoring does not cause a step down; the tick simply records that the subject stopped contributing data at that time point.

You compare two Kaplan-Meier survival curves by plotting them on the same axes and looking at how far apart and how separated they stay over time. A log-rank test is typically used to assess whether the difference between the groups is statistically significant rather than relying on the curves alone.

You can generate a Kaplan-Meier survival curve on SciFig: describe your groups and survival data and the generator produces a stepwise KM survival curve with censoring tick marks and a legend. You then relabel the axes, add a number-at-risk table, and export it for your manuscript.

The number-at-risk table beneath a Kaplan-Meier survival curve lists how many subjects remain in each group and are still being followed at successive time points. It helps readers judge how reliable the curve is later in follow-up, when few subjects remain and the estimate becomes less precise.