Scatter plotting as a simple tool to analyse relative organ to body weight in toxicological bioassays

In toxicological bioassays, organ weight is often expressed as a ratio to body weight or another denominator to account for natural differences in animal sizes. However, the relationship of treatment-induced organ and body weight change is complicated and relative weights may accordingly confound a toxicological assessment. In addition, the statistical assessment of relative weights is challenging. The examples given in this document show that toxicological interpretation of organ weight data in relation to body weight can be vastly improved by simple bivariate scatter plotting. Conversely, plots of relative organ weight are of limited value and may lead to an incorrect interpretation of toxic effects when used in isolation. Scatter plots are useful for qualitative hazard characterization and to generate hypotheses. Bivariate summary statistics indicate effect levels and help to explore the actual correlation of organ to body weight.