Statistical analysis for toxicity studies.

Generally, multiple statistical analysis methods can be applied for certain kind of data, and conclusion could differ, depending on the selected statistical method. Therefore, it is necessary to fully understand the performance of each statistical method and to examine which method is appropriate to use and to standardize statistical methods for toxicity studies to be carried out routinely. Several viewpoints for selecting appropriate statistical methods are discussed in this review paper. According to the distribution form, i.e., whether a distribution has a bell shape without outliers or not, either a parametric or a nonparametric approach should be selected. The nonparametric approach is also available for categorical data. Depending on the design and purpose of a study, several forms of statistical analysis are available. Assuming dose dependency, comparisons with a control are conducted by Williams test (nonparametric: Shirley-Williams test). When a dose dependent relationship is not expected, comparisons with the control are conducted by Dunnett test (nonparametric: Steel test). All possible pairwise comparisons among groups are conducted by Tukey test (nonparametric: Steel-Dwass test). If we are interested in several specific comparisons among groups, the Bonferroni-adjusted Student's -test (nonparametric: the Bonferroni-adjusted Wilcoxon test) can be used.