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A Multivariate Approach to Determine the Dimensionality of Human Facial Asymmetry

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This article reports on a demonstration in a multivariate context that the conventional method of directional asymmetry (DA) correction does not adequately compensate for the effects of DA in other dimensions of asymmetry.


Many studies have suggested that developmental instability (DI) could lead to asymmetric development, otherwise known as fluctuating asymmetry (FA). Several attempts to unravel the biological meaning of FA have been made, yet the main step in estimating FA is to remove the effects of directional asymmetry (DA), which is defined as the average bilateral asymmetry at the population level. The findings of the current study appear to be due to the presence of between-individual variation along the DA dimension. Consequently, the authors propose to decompose asymmetry into its different orthogonal dimensions, where a new measure of asymmetry is indicated, namely fluctuating directional asymmetry (F-DA). This measure describes individual variation in the dimension of DA, and can be used to adequately correct the asymmetry measurements for the presence of DA. This research provides evidence that this measure can be useful in disentangling the different dimensions of asymmetry, and further studies on this measure can provide valuable insight into the underlying biological processes leading to these different asymmetry dimensions. (publisher abstract modified)

Date Published: January 1, 2020