Editing Survival analysis (section)

====Kaplan–Meier plot for the aml data====

The [[survival function]] ''S''(''t''), is the probability that a subject survives longer than time ''t''. ''S''(''t'') is theoretically a smooth curve, but it is usually estimated using the [[Kaplan–Meier estimator|Kaplan–Meier]] (KM) curve. The graph shows the KM plot for the aml data and can be interpreted as follows:

*The ''x'' axis is time, from zero (when observation began) to the last observed time point.
*The ''y'' axis is the proportion of subjects surviving. At time zero, 100% of the subjects are alive without an event.
*The solid line (similar to a staircase) shows the progression of event occurrences.
*A vertical drop indicates an event. In the aml table shown above, two subjects had events at five weeks, two had events at eight weeks, one had an event at nine weeks, and so on. These events at five weeks, eight weeks and so on are indicated by the vertical drops in the KM plot at those time points.
*At the far right end of the KM plot there is a tick mark at 161 weeks. The vertical tick mark indicates that a patient was censored at this time. In the aml data table five subjects were censored, at 13, 16, 28, 45 and 161 weeks. There are five tick marks in the KM plot, corresponding to these censored observations.