LIFETEST Procedure
A common feature of lifetime or survival data is the presence of rightcensored observations due either to withdrawal of experimental
units or to termination of the experiment. For such observations, you know only that the lifetime exceeded a given value; the exact
lifetime remains unknown. Such data cannot be analyzed by ignoring the censored observations because, among other considerations,
the longerlived units are generally more likely to be censored. The analysis methodology must correctly use the censored observations
in addition to the uncensored observations. The LIFETEST procedure computes nonparametric estimates of the survivor function either by
the productlimit method (also called the KaplanMeier method) or by the lifetable method (also called the actuarial method).
The following are highlights of the LIFETEST procedure's features:
 estimates the probability density function (lifetable method )
 produces the NelsonAalen estimates of the cumulative hazards and the corresponding standard errors
 performs nonparametric analysis of competingrisks data
 provides nonparametric ksample tests based on weighted comparisons of the estimated hazard rate
of the individual population under the null and alternative hypotheses
 enables you to specify the following tests:
 logrank test
 Wilcoxon test
 TaroneWare test
 PetoPeto test
 modified PetoPeto test
 FlemingHarrington G_{ρ} family of tests
 provides corresponding trend tests to detect ordered alternatives
 provides stratified tests to adjust for prognostic factors that affect the events rates in the various populations

 provides a likelihood ratio test, based on an underlying exponential model to compare the survival curves of the samples
 computes censored data linear rank statistics based on the exponential scores (logrank test) and the Wilcoxon scores (Wilcoxon test)
 provides five transformations to be used in the calculation of confidence limits for the quartiles of survival time
 supports weighted estimation
 performs BY group processing, which enables you to obtain separate analyses on grouped observations
 creates a SAS data set that corresponds to any output table
 automatically creates graphs by using ODS Graphics

For further details see the SAS/STAT User's Guide:
The LIFETEST Procedure
( PDF  HTML )
Examples