Transgenic lambda/lacI mutagenicity assay: statistical determination of sample size

Statistical analysis of the lambda/lacI transgenic mutagenicity assay was used to determine optimal sample size and resource allocation in terms of number of animals and number of recovered target genes (recovered phage) required to demonstrate a statistically significant induction in mutant frequency. Statistical assumptions as applied to mutagenicity data are discussed for a number of frequently used statistical analyses. Log transformations are suggested as a means of meeting statistical assumptions and examples are given on interpreting results of analyses of log transformed data. The data analyzed in this study indicate that 300,000 lambda plaques from each of five animals should be analyzed per treatment group in order to detect a doubling of mutant frequencies. Additional sensitivity is gained primarily through increase of animal number and not the number of phage rescued, due to inherent animal-to-animal variability.