The ADJUST=DUNNETT DIFF=CONTROL(...) options on the STRATA statement in PROC LIFETEST do not always use the specified control level.

For unstratified k-sample tests (when the GROUP= option is NOT specified), the control level for the Dunnett multiple comparisons specified in DIFF=CONTROL(...) works correctly if there is only one STRATA variable. If there are two or more STRATA variables, only the first STRATA variable is used; that is, the first stratum that matches the first specified string in DIFF=CONTROL(...) is used as the control.

For stratified tests (where the GROUP= option is specified), there are two scenarios:

1) If the number of groups is less than or equal to the number of strata, the control level is always the first group regardless of what is specified in DIFF=CONTROL(...).

2) If the number of groups is larger than the number of strata, this will result in a Read Access Violation error and possibly freeze up the SAS session.

Since the default is to use the first stratum or group, the workaround is to use the default, e.g. - DIFF=CONTROL, and a format that designates the control as the first stratum or group.