Observations with a missing value for either the failure
time or the censoring variable are not used in the analysis.
If a stratum variable value is missing, survival function
estimates are computed for the strata labeled by the missing
value, but these data are not used in any rank tests.
However, the MISSING option can be used to request
that missing values be treated as valid stratum values.
If any variable specified in the TEST statement
has a missing value, that observation is not
used in the calculation of the rank statistics.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.