COMPARE Subcommand (KM command)

COMPARE compares the survival distributions for the different levels of the factor. Each of the keywords specifies a different method of comparison.

  • COMPARE is valid only when a factor variable is specified. If no factor variable is specified, KM issues a warning and COMPARE is not executed.
  • COMPARE uses whatever tests are specified on the TEST subcommand. If no TEST subcommand is specified, the log rank test is used.
  • If COMPARE is not specified, the default is OVERALL and POOLED. All factor levels are compared across strata in a single test. The test statistics are displayed after the summary table at the end of output.
  • Multiple COMPARE subcommands can be specified to request different comparisons.

    OVERALL. Compare all factor levels in a single test. OVERALL, together with POOLED, is the default when COMPARE is not specified.

    PAIRWISE. Compare each pair of factor levels. KM compares all distinct pairs of factor levels.

    POOLED. Pool the test statistics across all strata. The test statistics are displayed after the summary table for all strata. POOLED, together with OVERALL, is the default when COMPARE is not specified.

    STRATA. Compare the factor levels for each stratum. The test statistics are displayed for each stratum separately.

  • If a factor variable has different levels across strata, you cannot request a pooled comparison. If you specify POOLED on COMPARE, KM displays a warning and ignores the request.

Example

KM LENGTH BY SEXRACE
 /STATUS=EMPLOY EVENT (1) LOST (3,5 THRU 8)
 /STRATA=LOCATION
 /TEST = BRESLOW
 /COMPARE = PAIRWISE.
  • TEST specifies the Breslow test.
  • COMPARE uses the Breslow test statistic to compare all distinct pairs of SEXRACE values and pools the test results over all strata defined by LOCATION.
  • Test statistics are displayed at the end of output for all strata.