STUDY DESIGN AND SAMPLE SIZES FOR A LACL TRANSGENIC MOUSE MUTATION ASSAY

Design features that adjust and account for excess variation in a tran sgenic mouse mutation assay based on a loci target transgene from E. c oli ore considered. These features include proper identification of pl ate, packaging reaction, and animal identifier codes throughout the ex perimental and analysis phases of the study, ''blocking'' of exposed a nd unexposed animals when preparing and plating multiple packaging rea ctions from the same genomic DNA sample, separating sectored mutant pl aques and complete mutant plaques before performing any quantitative a nalyses, and testing for sources of excess variation attributable to f eatures of the experimental protocol-such as plate-to-plate (within pa ckaging reactions), packaging reaction-to-packaging reaction (within a nimals), and animal-to-animal (within study). Control and ethylnitroso urea-treated animal data are presented from a fully designed study in the lad assay. The study design incorporates many of these experimenta l principles. Statistical methods to identify excess variability are n oted, and the designed study data are used to illustrate the types of variability encountered in practice. A standard statistical test for t wo-sample testing is highlighted, from which recommendations are made for sample size selection in future studies. (C) 1995 Wiley-Liss, Inc.