A Kaplan-Meier curve estimates the probability of remaining event-free over time. Each downward step occurs when an observed event happens; a censoring mark records a participant whose follow-up ended without the event being observed.
The number-at-risk table shows how many participants remain under observation just before selected time points. It gives essential context for the sparse tail of a curve, where a large-looking step may be based on only a few participants.
For two or more groups, a log-rank test evaluates whether their complete survival experiences differ. It is an unadjusted comparison, not a causal estimate, and it does not replace a prespecified Cox model when covariate adjustment is required.
Time
The non-negative follow-up duration for each participant.
Event status
Whether the endpoint was observed or the record was right-censored.
Group
An optional treatment arm, cohort, stage, or other prespecified stratum.
Risk set
Participants still observed and event-free immediately before each event time.











