Abstract
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.
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Notes
Friendly et al. (2013), http://datavis.ca/papers/ellipses.pdf.
Bagplots can be generated using, e.g. R software and the aplpack package by H. P. Wolf or ggplot2 together with some functions that are hosted on Ben Marwick’s GitHub repository.
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Acknowledgements
I would like to thank the following people for educational discussions related to relative organ weights and associated issues: Dr. Stanley E. Lazic, AstraZeneca, for general discussions and the development of Bayesian models to assess toxic effects. Prof. Christian Ritz, University of Copenhagen, with regard to benchmark dose modelling and, Prof. Ludwig A. Hothorn for discussing different statistical methods to statistically compare relative organ weights.
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Kluxen, F.M. Scatter plotting as a simple tool to analyse relative organ to body weight in toxicological bioassays. Arch Toxicol 93, 2409–2420 (2019). https://doi.org/10.1007/s00204-019-02509-3
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DOI: https://doi.org/10.1007/s00204-019-02509-3