You can specify covariates in the TEST statement. For example, consider the results of a small randomized trial on rats. Suppose you assign forty rats exposed to a carcinogen into two treatment groups. The event of interest is death from cancer induced by the carcinogen. The response is the time from randomization to death.
Interest lies in whether the survival distributions differ between the two treatments.
In the TIME statement, the survival time variable, Days , is crossed with the censoring variable, Status , with the value 0 indicating censoring. If the exponential model is appropriate, the LS curve should be approximately linear through the origin. If the Weibull model is appropriate, the LLS curve should be approximately linear. Since there are more than one stratum, the LLS plot may also be used to check the proportional hazards model assumption. Under this assumption, the LLS curves should be approximately parallel across strata.