Power calculations for detecting interaction in stratified 2 x 2 tables

Given several 2 x 2 contingency tables, the first step in epidemiologic research is to test for homogeneity of odds ratios across these tables. A. second problem of equal interest, but often overlooked, is to evaluate the power of detection of interaction if it is present. We address the latter issue in the context of 2 x 2 contingency tables. For the 2 x 2 x 2 case, given the marginal totals and the odds ratios for the respective two tables, we provide a closed form power formula for the rejection of the null hypothesis of homogeneity of the odds ratios. For several 2 x 2 tables, we provide a resampling approach to assessing the power for detecting interaction, if present. (C) 1999 Published by Elsevier Science B.V. All rights reserved.