KaplanMeierkäyriä

Kaplan Meierkäyriä are a non-parametric statistical method used to estimate the survival function from lifetime data. This method accounts for the time from an initial point until one of two things occurs: either the event of interest (e.g., death, disease recurrence) happens, or the study participant is lost to follow-up or the study ends before the event occurs. The curve visually represents the probability of survival over time.

The calculation of a Kaplan-Meier curve starts at time zero with a survival probability of 1. As time progresses, the curve drops at each observed event. The size of the drop is inversely proportional to the number of individuals still at risk at that specific time. Specifically, if an event occurs at time t, and there are n individuals still at risk just before time t, the estimated survival probability at time t is calculated by multiplying the survival probability just before t by (n-1)/n. This ensures that censored observations (lost to follow-up or end of study) do not unduly influence the survival probability at those specific time points.

Kaplan-Meier curves are particularly useful for comparing survival experiences between different groups. For instance, one might compare the survival curves of patients receiving different treatments. Statistical tests, such as the log-rank test, are often used in conjunction with Kaplan-Meier curves to determine if the observed differences in survival between groups are statistically significant. The method is widely applied in medicine, biology, and engineering.