RE: “EASY SAS CALCULATIONS FOR RISK OR PREVALENCE RATIOS AND DIFFERENCES”

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Abstract
In their editorial, Spiegelman and Hertzmark (1) recommend an easy method to estimate risk and prevalence ratios, and they include SAS macros for performing the calculations. The method uses maximum likelihood when the correct binomial model converges and a Poisson model with a robust variance estimator when the correct model fails to converge. We agree completely with using maximum likelihood estimators (MLEs) when the model converges. However, one can do better than the Poisson model when the correct model fails to converge.