SAS/STAT Software

LIFETEST Procedure

A common feature of lifetime or survival data is the presence of right-censored 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 longer-lived 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 product-limit method (also called the Kaplan-Meier 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 (life-table method )
  • produces the Nelson-Aalen estimates of the cumulative hazards and the corresponding standard errors
  • performs nonparametric analysis of competing-risks data
  • provides nonparametric k-sample 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:
    • log-rank test
    • Wilcoxon test
    • Tarone-Ware test
    • Peto-Peto test
    • modified Peto-Peto test
    • Fleming-Harrington Gρ 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 (log-rank 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