STRATA Statement |
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 of death; the first level of the stratification variable might represent weeks 052, the second might represent weeks 5380, and so on. In multicenter clinical studies, each level of the stratification variable might represent a particular center.
The following option is available in the STRATA statement after a slash (/):
specifies the type of strata weighting to use when computing the Freeman-Tukey and t tests. Valid keywords are SAMPLESIZE, HARMONIC, and EQUAL. SAMPLESIZE requests weights proportional to the within-stratum sample sizes, and is the default method even if the WEIGHT= option is not specified. HARMONIC sets up weights equal to the harmonic mean of the nonmissing within-stratum CLASS sizes, and is similar to a Type 2 analysis in PROC GLM. EQUAL specifies equal weights, and is similar to a Type 3 analysis in PROC GLM.