Assessment of sex differences for multifactorial traits using path analysis: application to learning difficulties.

A general model of multifactorial inheritance is described which allows for sex-specific transmission from parent to offspring, sex-specific correlations in the rearing environments of full siblings, and different prevalences for males and females for qualitative traits. Formulas for the correlations between several types of relatives are given in terms of an underlying path model, and a computer program, available upon request, is described. The model is applied to the Collaborative Perinatal Project sample of siblings and first cousins of children with learning difficulties. No sex differences were found either in transmission or in correlated sibling environments for learning difficulties. Evidence is given that the correlation between the rearing environments of siblings is negative, possibly due to differential allocation and family resources.