Design of a statistical method for the analysis of mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase locus of cultured Chinese hamster ovary cells.

Mutagenesis data collected in the mammalian cell CHO/HGPRT assay were analyzed to study the distribution of the experimental errors associated with the test. The data neither followed the widely assumed Poisson distribution nor satisfied the usual statistical assumptions of normality and homogeneous variance of experimental errors. We transformed the data by using the power formula Y = (X + A) gamma where X is the observed mutation frequency, Y is the transformed frequency, and A and gamma are constants determined by the procedure of Box and Cox. Setting A = 1 and gamma = 0.15 we produced transformed values for which the assumptions of homogeneous variance and normal distribution were satisfied. This transformation enables one to properly use Student's t-test and dose-response analysis of variance to analyze CHO/HGPRT results. The experimental design for CHO/HGPRT mutagenesis assays is also discussed.