Procedures

We examined the modifying effects of nurturing care in the home on the association between cumulative adversities and adolescent human capital (panel).

Outcome (human capital)

1993 Pelotas Birth Cohort

Birth to Twenty Plus (Bt20+) Birth Cohort

Effect modifier (nurturing care in the home)

1993 Pelotas Birth Cohort

Bt20+ Birth Cohort

Cumulative adversities

1993 Pelotas Birth Cohort

Bt20+ Birth Cohort

Human capital is defined as the education, training, skills, and health that contribute to economic and other forms of productivity and social integration.²⁰ We included the domains of adolescent IQ, psychosocial adjustment, and height assessed with differing, but conceptually equivalent, methods. In the 1993 Pelotas cohort, IQ at age 18 years was assessed using four subtests of the Wechsler Adult Intelligence Scale (WAIS-III short form; n=4050), namely similarities, picture completion, arithmetic, and symbol coding. The WAIS-III score was adapted and standardised for Brazil and normalised for analysis. In the Bt20+ cohort, cognitive development was assessed with the Raven's Standard Progressive Matrices test at age 16 years (n=1373). This test measures non-verbal cognitive functioning and has been used widely, including in South Africa.²¹ We measured psychosocial adjustment with reverse scaling of internalising and externalising problems.²² In the 1993 Pelotas cohort, psychosocial problems were assessed at age 15 years with the Strengths and Difficulty Questionnaire (SDQ) parent version, a brief screening tool adapted and validated for Brazil.²³ Mothers answered 20 questions representing internalising and externalising items about their adolescents' behaviours. Parental responses are valid for assessing adolescents' internalising and externalising behaviours.²⁴ In the Bt20+ cohort, the 112-item Youth Self-Report²⁵ was completed by adolescents at age 14 years. Behaviours were rated on a 3-point scale (from not true [score 1] to often true [score 3]). For this analysis, we used the 12-item anxiety (internalising) and 14-item aggression–oppositionality (externalising) items that are most comparable with the SDQ items. For both cohorts, the questionnaires referenced the preceding 6 months. We summed the reverse-scaled items to generate scores denoting positive psychosocial adjustment, consistent with the direction of the other two measures of human capital. Standing heights were assessed using stadiometers in the 1993 Pelotas cohort at age 18 years, and at age 16 years in the Bt20+ cohort, matching the ages of IQ measurement. Heights were converted to Z scores using age-specific and sex-specific WHO standards.²⁶

In the 1993 Pelotas cohort, the 55-item Early Childhood Home Observation for Measurement of the Environment (EC-HOME) inventory was done in a subsample (n=632) at age 4 years.²⁷ Items were scored as 0 or 1 if absent or present, respectively, as observed by trained data collectors or reported by mothers. Sample items were learning subscale²⁷ (ie, “Child is helped to learn shapes and sizes at home”) and language subscale (ie, “The caregiver sings to the child daily”). We summed the two subscales in 18-item learning opportunities scores. The items evaluating responsiveness included verbal caregiver–child interactions (eg, “Parent converses with child at least twice during visit”). We summed the items to create 7-item responsive caregiving scores, as predetermined by the EC-HOME. In the Bt20+ cohort, responsive caregiving and learning opportunities were assessed at age 2 years (n=1838) with age-appropriate questions similar to EC-HOME. Responsiveness was based on a 6-item questionnaire from the EC-HOME completed by interviewer observation (eg, “Does the child appear happy, confident, and secure in the mother's presence?”). Learning opportunities were based on a 5-item questionnaire (eg, “Is there anything you are trying to teach your child at the moment?”). All measures were coded with higher scores denoting higher nurturance.

Early adversities were mother–child assessments during the perinatal period, infancy, and early childhood in the 1993 Pelotas and Bt20+ cohorts, before assessments of the nurturing care components.² Measures were chosen a priori based on developmental theory⁶ and availability in the two datasets. No available adversity measures were excluded. Each measure contributed equally to the index. The environmental cumulative adversities index included: low-income household (lowest two wealth quintiles within each site); low maternal schooling (grades of schooling attainment below 60th percentile); short maternal stature (<150·1 cm, representing −2 height-for-age Z score below international standards²⁸); maternal age at child's birth (<18 years); poor maternal mental health (self-report questionnaire in the 1993 Pelotas cohort [>7 points] at child age 4 years,²⁹ and 24-item Pitt Depression Inventory in the Bt20+ cohort [≥20 points³⁰] at child age 6 months); and household crowding (more than three people per room, UN threshold). Each child's environmental cumulative adversities index was summed, ranging from 0–6 points. The child cumulative adversities index included: low birthweight (<2500 g), preterm birth (<37 weeks), and stunted growth at 12 months (length-for-age Z score less than −2 relative to international standards²⁶). The child cumulative adversities index ranged from 0–3 points. The total early cumulative adversities index is the sum of the environmental and child adversities (range 0–9), with higher scores denoting more adversities.