Family income in early childhood and subsequent Attention-Deficit/Hyperactivity Disorder: A quasi-experimental study
Studies have found negative associations between socioeconomic position and attention deficit/hyperactivity disorder (ADHD), but it remains unclear if this association is causal. The aim of this study was to determine the extent to which the association between family income in early childhood and subsequent ADHD depends on measured and unmeasured selection factors.
A total of 811,803 individuals born in Sweden between 1992 and 2000 were included in this nationwide population-based cohort study. Diagnosis of ADHD was assessed via the Swedish national Patient Register and the Swedish Prescribed Drug Register. Annual family income during offspring's first 5 years in life was collected prospectively from the Swedish Integrated Database for Labour Market Research and divided into quartiles by (lower) family disposable income. We predicted ADHD from family income while controlling for covariates and also comparing differently exposed cousins and siblings to control for unmeasured familial confounding.
The crude analyses suggested that children exposed to lower income levels were at increased risk for ADHD (HRQuartile1 = 2.52; 95% CI, 2.42–2.63; HRQuartile2 = 1.52; 95% CI, 1.45–1.58; HRQuartile3 = 1.20; 95% CI, 1.14–1.15). This dose-dependent association decreased after adjustment for measured covariates (HRQuartile1 = 2.09; 95% CI, 2.00–2.19; HRQuartile2 = 1.36; 95% CI, 1.30–1.42; HRQuartile3 = 1.13; 95% CI, 1.08–1.18). Although the association was attenuated in cousin comparisons (HRQuartile1 = 1.61; 95% CI, 1.40–1.84; HRQuartile2 = 1.28; 95% CI, 1.12–1.45; HRQuartile3 = 1.14; 95% CI, 1.01–1.28) and sibling comparison models (HRQuartile1 = 1.37; 95% CI, 1.07–1.75; HRQuartile2 = 1.37; 95% CI, 1.12–1.68; HRQuartile3 = 1.23; 95% CI, 1.04–1.45), it remained statistically significant across all levels of decreased disposable family income.
Our results indicated that low family income in early childhood was associated with increased likelihood of ADHD. The link remained even after controlling for unmeasured selection factors, highlighting family income in early childhood as a marker of causal factors for ADHD.
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ABSTRACT: This article draws upon theories of the life course and child development to examine how structural changes in the family and parenting practices affect child behavior problems in middle childhood. Our analysis improves upon prior research by simultaneously examining the effects of poverty, single-motherhood, welfare, and kin co-residence, distinguishing between early and current exposure to changes of these family conditions, and controlling for unobserved, preexisting family differences. We estimate fixed-effects sibling models using the matched mother–child data of NLSY79. We find two robust relationships: child behavior problems are shaped by early childhood poverty, which is not mediated by current parenting nor contaminated by family selection, and mothers’ use of physical punishment, which is not contaminated by family selection. The findings support the early childhood exposure hypothesis applied to poverty, a parenting hypothesis applied to mother’s physical punishment, and a family selection hypothesis applied to positive parenting, father’s time, and cultural activities.Social Science Research. 06/2006;
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ABSTRACT: Low birth weight (LBW) is associated with attention problems (AP) and attention-deficit/hyperactivity disorder (ADHD). The etiology of this association is unclear. We investigate whether there is a causal influence of birth weight (BW) on AP and whether the BW effect is mediated by catch-up growth (CUG) in low-BW children. Longitudinal data from >29,000 twins registered with the Netherlands Twin Register with BW ≥1,500 g and gestational age (GA) ≥32 weeks were analyzed with the cotwin control method. Hyperactivity and AP were assessed at ages 3, 7, 10, and 12 years; weight was assessed at birth and age 2 years. Children in the lowest BW category of 1,500 to 2,000 g scored 0.18 to 0.37 standard deviations (SD) higher on AP than children in the reference category of 3,000 to 3,500 g. This effect was present in term-born and preterm-born children. Importantly, in BW discordant monozygotic (MZ), dizygotic (DZ), and unrelated (UR) pairs, the child with the lower BW scored higher on hyperactivity and AP than the child with the higher BW and within-pair differences were similar for MZ, DZ, and UR pairs. This pattern is consistent with a causal effect of BW on AP. MZ and DZ twin pairs concordant for LBW but discordant for CUG showed similar AP scores, thus ruling out any effect of CUG on AP. These results strongly indicate that the association of birth weight and AP represents a causal relationship. The effects of BW are not explained by CUG in LBW children.Journal of the American Academy of Child and Adolescent Psychiatry 12/2011; 50(12):1247-54.e2. · 4.98 Impact Factor
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ABSTRACT: To test the hypothesis that psychosocial adversity in the family predicts medicated ADHD in school children. ADHD-medication during 2006 was identified in the Swedish Prescribed Drug Register in national birth cohorts of 1.1 million 6-19 year olds. Logistic regression models adjusted for parental psychiatric disorders were used to test our hypothesis. There was a clear gradient for ADHD medication with level of maternal education, with an adjusted odds ratio of 2.20 (2.04-2.38) for the lowest compared with the highest level. Lone parenthood and reception of social welfare also implied higher risks of ADHD-medication with adjusted ORs of 1.45 (1.38-1.52) and 2.06 (1.92-2.21) respectively. Low maternal education predicted 33% of cases with medicated ADHD and single parenthood 14%. Social adversity in the family predicts a considerable proportion of ADHD-medication in school children in Sweden.Acta Paediatrica 12/2009; 99(6):920-4. · 1.97 Impact Factor