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: In the 1950's, many experts believed hyperkinesis was a neurotic reaction to inner conflicts arising from early family experiences. In the 1990's, many experts believed ADHD to be ‘genetic’ (without a mechanistic explanation of what that meant). Both views appear naïve today in a scientific world grappling with the complexity of highly plastic gene expression, gene x environment interplay, and epigenetic, context-dependent emergence of psychopathology. Both views also fail to account for the uncomfortable fact that ADHD is also associated with social disadvantage – a level of analysis required in a developmental psychopathology approach. That developmental psychopathology approach, pioneered a generation ago, initially emphasized the accumulation of risk and protective factors, and emerged in a contemporary systemic approach that seeks to determine whether it is risk accumulation (e.g., allostatic load) or specific risk factors (e.g., family process) that mechanistically shape psychopathology. Despite the prominence of the developmental psychopathology perspective, the social context of ADHD is surprisingly neglected today. Both Russell et al. (this issue, 2014) and Larsson et al. (this issue, 2014) take strides toward remedying this state of affairs.Journal of Child Psychology and Psychiatry 05/2014; 55(5). · 5.42 Impact Factor