Use of statistics when examining lifetime studies in rodents to detect carcinogenicity.

The lifetime assay for carcinogenicity that subjects groups of 50 animals per sex per dose to three doses and a control is examined for its statistical properties. Using the standard formulation of tests of hypothesis, it is shown that there is a 20-50% chance of having a false positive and that it is possible to define a "weak carcinogen" in terms of the degree of effect that would produce a false negative less than 5% of the time. Whether hypothesis testing is a proper use of statistics in this context is questioned, and alternatives are proposed.