Multivariate statistical analysis of organ weights in toxicity studies

Toxicity studies with drugs in animals are performed to establish the toxic ity profile including the no-toxic-effect-level in the animals. One of the responses used in the search for effects is organ weight. Since organ weigh t is related to body weight of the animal, the analysis of organ weight has to be adjusted. A traditional analysis of covariance with body weight as c ovariate is not always appropriate since the body weight itself can be affe cted by the test compound. Hence, a multivariate analysis of variance is su ggested, where the correlation between organ weight and body weight is take n into account in testing an overall treatment effect. Two dimensional plot s of the contour curves are used to visualize the treatment effect on organ weight and body weight simultaneously. The test procedure suggested for co mparing differences between control and treated groups of animals is: start by testing hypotheses of equality of covariance matrices for the different treatment groups and then, depending on the results from the first test, t est equality of the mean vectors. (C) 1999 Elsevier Science Ireland Ltd. Ai l rights reserved.