The SURVEYPHREG Procedure

STRATA Statement

STRATA variables </ option> ;

The STRATA statement names variables that form the strata in a stratified sample design. The combinations of levels of STRATA variables define the strata in the sample, where strata are nonoverlapping subgroups that were sampled independently.

If your sample design has stratification at multiple stages, you should identify only the first-stage strata in the STRATA statement. See the section Specifying the Sample Design for more information.

If you provide replicate weights for BRR or jackknife variance estimation with a REPWEIGHTS statement, you do not need to specify a STRATA statement.

The STRATA variables are one or more variables in the DATA= input data set. These variables can be either character or numeric, but the procedure treats them as categorical variables. The formatted values of the STRATA variables determine the STRATA variable levels. Thus, you can use formats to group values into levels. See the discussion of the FORMAT procedure in the Base SAS Procedures Guide and the discussions of the FORMAT statement and SAS formats in the SAS Formats and Informats: Reference. Strata variables must not occur in the CLASS statement.

The STRATA statement in PROC SURVEYPHREG is different from the STRATA statement in PROC PHREG (Chapter 67: The PHREG Procedure,). PROC PHREG fits different baseline hazard functions in different strata, which is useful if the proportional hazards assumption is not satisfied.

You can specify the following option in the STRATA statement after a slash (/):

LIST: displays a “Stratum Information” table, which lists all strata together with the corresponding values of the STRATA variables. This table provides the number of observations and the number of clusters in each stratum, as well as the sampling fraction if you specify the RATE= or TOTAL= option.