U.S. flag

An official website of the United States government, Department of Justice.

A Multivariate Approach to Determine the Dimensionality of Human Facial Asymmetry

NCJ Number
O. Ekrami; et al
Date Published

This project demonstrated in a multivariate context that the conventional method of correcting directional asymmetry (DA) 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. In the current study, the failure of the conventional method of DA correction to adequately compensate for the effects of DA in other dimensions of asymmetry appeared to be due to the presence of between-individual variation along the DA dimension. Consequently, the researchers decomposed asymmetry into its different orthogonal dimensions, introducing a new measure of asymmetry, 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. The project provides evidence that this measure can be useful in disentangling the different dimensions of asymmetry. 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