Cumulative environmental risk scores were created based on maternal reports. Risk items were organized into one of three developmental eras so as to coincide with the OXTR methylation data: (i) prenatal risks, (ii) early childhood risks (birth – age 7), and (iii) mid-childhood risks (age 8–9). For each developmental period, items were summed to create five conceptually distinct but related risk domains: (i) Life events (e.g. death in family, accident, illness), (ii) Contextual risks (e.g. poor housing conditions, financial problems), (iii) Parental risks (e.g. parental psychopathology, criminal involvement and substance use), (iv) Interpersonal risks (e.g. intimate partner violence, family conflict), and (v) Direct victimization (e.g. child bullied by peers or physically hurt ; available postnatally). Risk domains were positively and significantly correlated, both within and between developmental periods. We used confirmatory factor analyses (CFAs) to assess the internal reliability of the risk domains and to extract one global cumulative risk score for each developmental period, showing good model fit. Higher scores indicate greater environmental risk exposure. See SI 6–9 for full item descriptions, details of inter-correlations between risk domains and factor analysis fit indices.
