Breslow N E (Department of Biostatisties, SC-32, University of Washigton, Seattle, WA 98195, USA). Elementary methods of cohort analysis. International Journal of Epidemiology 1984, 13: 112– 115. The Mantel-Haenszel procedure offers a simple and efficient means of estimating a common rate ratio from incidence density data in cohort studies. A new formula is provided for the variance of its logarithm, comparisons are made with the method of maximum likehood, and associated tests for heterogeneity and trend in the component rate ratios are described.