Tests for homogeneity of the risk ratio in a series of 2 x 2 tables

We often apply the risk ratio to measure the strength of a causal relations hip between a suspected risk factor and a disease of interest. In this pape r we consider testing the homogeneity of risk ratio over a series of 2 x 2 tables, In addition to the classical weighted least squares (CWLS) test pro cedure, we consider two test procedures using simple transformations of the CWLS statistic and develop three other asymptotically weighted test proced ures. On the basis of Monte Carlo simulation, we conclude that the commonly -used CWLS test procedure is generally conservative, especially when the nu mber of 2 x 2 tables is large and the mean group size per table is moderate or small. We further find that two of the test procedures discussed here c an not only generally outperform the CWLS test procedure, but also perform well in a variety of situations considered in this paper. Finally, we illus trate the use of these testing procedures with an example of six randomized trials that assess the effects of aspirin on the prevention of death in po st-myocardial infarction patients. Copyright (C) 2000 John Wiley & Sons, Lt d.