
Researchers mostly use Gaussian and lognormal distributions to model biological traits. When considering infant birth weight and gestational age cohorts, we looked at a general twocomponent hybridlognormal mixture model. We found that all of the twocomponent mixture models provide reasonable approximations to birth weight and gestational age distributions. Specifically, birth weight is best fit with a twocomponent hybridlognormal and gestational age is best fit by a mixture of two Gaussian components. In the case of particular populations, the sum of twoGaussian components provides the best fit except in the case of African American females where a Gaussian secondary component and a lognormal primary component fits birth weight better than the mixture of two Gaussians.

