Overall type I error rate and power of multiple Dunnett's tests on rodent body weights in toxicology studies.

Body weight data are routinely collected in in vivo general toxicology studies, including 2-year carcinogenicity studies, to help assess the overall health of animals. The effect of the compound on body weight is statistically evaluated for each sex separately using a linear trend test or a many-to-one test by Dunnett. These tests are performed either in the framework of a one-factor analysis of variance (ANOVA) or a repeated measures ANOVA. The one-factor ANOVA with Dunnett's test at each time point is a common practice in industry. Although each individual test is conducted at the 0.05 significance level, one wonders about the overall type I error rate and power for performing many individual Dunnett's tests. A simulation study is conducted to answer this question for general toxicology studies of durations 1 month, 3 months, and 2 years. These results provide guidance to managing multiplicity of body weight analysis of general toxicology studies.