From resulting propensity scores, a 5-level categorical variable was computed with each level containing approximately 20% of the propensity score distribution. Associations between parental separation and (i) family background characteristics and (ii) early-onset sex (defined as sex by age 15) were examined within quintiles, the latter conditional on successful matching on family background. Since PSA was conducted at the level of the family, statistical tests for associations with twin outcomes were adjusted for familial clustering.
