LIFETEST+ODS+IML=Stratified Log Rank Tests

When analyzing right-censored survival data, equality of survival curves across treatment groups is often tested using log rank tests (Peto and Peto 1972), aka Mantel-Haenszel tests. For instance, in a cancer trial, the primary response variable might be time to disease progression and the treatment groups might be chemotherapy regimens. To increase power and protect against baseline imbalances, you could stratify by a variable with known prognostic value, such as disease stage. But in versions 8 and earlier, proc LIFETEST performs unstratified log rank tests only. Sorting the input dataset by stratum and adding a "by stratum ;" statement yields the information you need to handcompute the stratified log rank statistic. By feeding ODS output datasets to SAS/IML, you can easily automate these computations and obtain exactly the same stratified log rank test p-values calculated by SPSS, Stata, and BMDP. Stratified generalized Wilcoxon tests and 1 df trend tests are a bonus.