We first calculated parental externalizing polygenic scores, parental externalizing disorder composite, and parenting related measures as the mean of mother and father on a given variable. In instances where information was only available for one parent, the available score was used. We employed this “midparent” approach for two reasons: (1) to make maximal use of the available data in order to maximize the sample size, and (2) because we made no specific hypotheses regarding maternal versus paternal genetic nurture effects. This strategy is also consistent with other prior studies of genetic nurturance (e.g., Saunders et al., 2021; Willoughby et al., 2021).
