STRATA
variables </ options> ;
The STRATA statement names the variables defining strata or representing matched or nested sets of individuals in a case-control study. Each STRATA variable can be either character or numeric, and the formatted values of the STRATA variables determine the levels. Thus, you can also use formats to group values into levels. See the discussion of the FORMAT procedure in the Base SAS Procedures Guide. At least one variable must be specified in order to invoke the stratified analysis. See the section Stratified Analysis for more information.
The following options can be specified after a slash (/):