In medical studies, the computation of a meaningful incidence rate frequently demands adjustment for covariates. One means for achieving such adjustment isstandardization.The (directly) standardized rate is calculated by using the appropriate weighted average of rates overstratadetermined by the covariates. Thus strata formation is crucial in obtaining good results. This article compares three competing methods for stratification using data from a drug study in which the incidence rate of a certain side effect is of interest. The techniques examined are (a) contingency-table cell aggregation, (b) classification trees, and (c) logistic regression. The relative merits of the three methods are discussed.