The STRATA statement identifies a single variable to use as a
stratification variable in the analysis. This yields tests similar
to those discussed in Mantel and Haenszel (1959) and Hoel and
Walburg (1972) for binary data and pooled-means tests for continuous
data. For example, when you test for prevalence in a carcinogenicity
study, it is common to stratify on intervals of the time at death;
the first level of the stratification variable may represent weeks
0-52, the second weeks 53-80, and so on. In multicenter
clinical studies, each level of the stratification variable may
represent a particular center.
- STRATA variable ;
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