Oecologia

, Volume 166, Issue 4, pp 961–971 | Cite as

Size correction in biology: how reliable are approaches based on (common) principal component analysis?

Population ecology - Original Paper

Abstract

Morphological traits typically scale with the overall body size of an organism. A meaningful comparison of trait values among individuals or populations that differ in size therefore requires size correction. A frequently applied size correction method involves subjecting the set of n morphological traits of interest to (common) principal component analysis [(C)PCA], and treating the first principal component [(C)PC1] as a latent size variable. The remaining variation (PC2–PCn) is considered size-independent and interpreted biologically. I here analyze simulated data and natural datasets to demonstrate that this (C)PCA-based size correction generates systematic statistical artifacts. Artifacts arise even when all traits are tightly correlated with overall size, and they are particularly strong when the magnitude of variance is heterogeneous among the traits, and when the traits under study are few. (C)PCA-based approaches are therefore inappropriate for size correction and should be abandoned in favor of methods using univariate general linear models with an adequate independent body size metric as covariate. As I demonstrate, (C)PC1 extracted from a subset of traits, not themselves subjected to size correction, can provide such a size metric.

Keywords

Bias Body size Morphology Multivariate statistics Shape 

Supplementary material

442_2011_1934_MOESM1_ESM.doc (44 kb)
Supplementary material 1 (DOC 44 kb)

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Zoological InstituteUniversity of BaselBaselSwitzerland

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