We conducted power calculations to compare different approaches (nonparametric, arcsine square root-transformed, logit-transformed, untransformed) for analyzing litter-based proportional data. A reproductive toxicity study with a control and one treated group provided data for two endpoints: prenatal loss, and fertility by in utero insemination (IUI). Type I error and power were estimated by 10,000 simulations based on two-sample one-tailed t-tests with varying numbers of litters per group. To further compare the different approaches, we conducted additional analyses with the mean proportions shifted toward zero to produce illustrative scenarios. Analyses based on logit-transformed proportions had greater power than those based on untransformed or arcsine square root-transformed proportions, or nonparametric procedures.