Logarithmic transformation bias in allometry
Article first published online: 27 APR 2005
Copyright © 1993 Wiley-Liss, Inc., A Wiley Company
American Journal of Physical Anthropology
Volume 90, Issue 2, pages 215–228, February 1993
How to Cite
Smith, R. J. (1993), Logarithmic transformation bias in allometry. Am. J. Phys. Anthropol., 90: 215–228. doi: 10.1002/ajpa.1330900208
- Issue published online: 27 APR 2005
- Article first published online: 27 APR 2005
- Manuscript Accepted: 16 JUL 1992
- Manuscript Received: 4 FEB 1992
- Lognormal distribution
It has been known for some time (DJ Finney, J. Roy. Stat. Soc. Suppl. 7:155–161, 1941) that transformation of an arithmetic data set to logarithms results in biased estimates when predicted values from a leastsquares regression are detransformed back to arithmetic units. Predicted values are estimates of the geometric mean of the dependent variable at that value of the independent variable, rather than the arithmetic mean. Since the geometric mean is always less than the arithmetic mean, detransformed predictions will underestimate the value in question. This bias affects the interpretations of allometric equations used for estimation, such as predicting fossil body mass from skeletal dimensions, and applications of allometry as a “criterion of subtraction,” in which residual variation is evaluated.
A number of parametric and nonparametric corrections for transformation bias have been developed. Although this problem is relatively unexplored in mammalian morphometrics, it has received considerable attention in other disciplines that use power functions structurally identical to the allometric equation. Insights into transformation bias and the use of correction terms from economics, limnology, forestry, and hydrology are reviewed and interpreted for application to mammalian allometry. © 1993 Wiley-Liss, Inc.