Linear and partially linear models of behavioural trait variation using admixture regression

Admixture regression methodology exploits the natural experiment of random mating between individuals with different ancestral backgrounds to infer the environmental and genetic components to trait variation across culturally-defined racial and ethnic groups. This paper provides a new statistical framework for admixture regression based on the linear polygenic index model widely used in behavioural genetics. Using this framework we develop a new test of the differential impact of multi-racial identities on trait variation, an orthogonalization procedure for added explanatory variables, and a partially linear semiparametric functional form. The methodology is illustrated with data from the Adolescent Brain Cognitive Development Study.