Design and analysis of experiments on mutagenicity. II. Assays involving microorganisms.

The design and statistical analysis of mutagenicity experiments involving microorganisms and a single dose of mutagen are discussed. Test statistics are derived for use in determining the mutagenicity of a chemical when survival data are available and also when such data are not available. One's likelihood (power) of correctly concluding a chemical is mutagenic is examined, and minimum total sample sizes required for 95% power are presented. It is found that one generally has greater power when survival data are available. Required precision is estimating survival is discussed in reference to type-1 and type-2 errors. The proper use of the formulae and figures presented is illustrated by examples.