A 2016 systematic review (Russell et al, 2016) found that lower socioeconomic status (SES) was associated with ADHD across multiple dimensions (i.e. income, maternal education, occupation, paternal education, single-parent families). The Elucidating Pathways of Child Health inequalities (EPOCH) study examined the relationship between household income, maternal education and childhood ADHD.
The EPOCH study, funded by the Canadian Institutes of Health Research, was developed by researchers in the International Network for Research on Inequalities in Child Health, who examined large, population-based birth cohorts from their respective countries that had comparable data aligned with UNICEF child well-being outcomes.
Here, data were extracted from seven birth cohorts participating in the EPOCH study.* All cohorts enrolled population-based samples of children at birth or within the first 2 years of life. ADHD was measured in late childhood according to Diagnostic and Statistical Manual of Mental Disorders – 4th Edition or International Statistical Classification of Diseases and Related Health Problems, 10th Revision criteria, with diagnoses based on parental self-report of medical diagnosis or diagnostic criteria, except for the Alla Barn i Sdöstra Sverige (ABIS) cohort from Southeast Sweden, for which ADHD diagnosis was derived from Swedish medical records.
The two main measurements of SES were maternal education and household income. Both were measured in the first 5 years of life and were available in all cohorts. $Purchasing Power Parity 2000 (OECD, 2000) were obtained for each cohort.
Prevalence of ADHD ranged from 1.3% (UK) to 7.6% (Quebec). Levels of maternal education at baseline varied by cohort, with the UK and Quebec having the highest prevalence of mothers with low education (20.8% and 28.6%, respectively), while Sweden and Australia had the lowest (8.4% and 9.0%, respectively). Australia and Canada (all provinces) had a larger proportion of mothers with higher education (47.8% and 42%, respectively) compared with the other cohorts. The proportion of mothers from ethnic minority groups, or born outside the cohort country, was lowest in Southeast Sweden and highest in the US (6.5% and 43.9%, respectively). Lastly, the proportion of mothers who were younger than 20 years of age at the time of their child’s birth was <10% in all cohorts except for the Canada cohort, in which the proportion was 23% and considered an outlier.
Pooled risk estimates (relating to a total of 44,925 children) were calculated for household income (low: 1.83, 95% confidence interval [CI] 1.38–2.41; middle: 1.25, 95% CI 1.01–1.54) and maternal education (low: 2.13, 95% CI 1.39–3.25; middle: 1.42, 95% CI 1.13–1.79). Heterogeneity ranged from moderate to high (I2: middle income, 21.8%; middle education, 47.9%; low income, 51.3%; low education, 79.8%).
Absolute inequality in ADHD during late childhood across cohorts confirmed the advantage for children in high-income households, or those with mothers with higher levels of education. The largest potential reduction in ADHD due to increased maternal education was observed in Australia and Sweden (4% and 3% reductions, respectively), whereas improvements in household income would lead to the largest reductions in ADHD prevalence in Quebec and Canada (6% and 5% reductions, respectively).
Several limitations to this study were identified, including the prevalence of ADHD varying widely, and ADHD criteria being based on parental reports in all but the ABIS cohort. It is possible that, due to the reliance on parental reporting, informant bias could have resulted in overreporting by parents of low SES.
The authors concluded that children who are in higher income households, or had more educated mothers, were at lower risk of ADHD between the ages of 9–11 years in high-income countries. Pooled risk estimates suggest that ADHD in later childhood is more strongly related to maternal education than household income. However, the authors noted that there is an association between early childhood SES and ADHD in later childhood, although the reason for this relationship remains unclear. The authors recommended that future research should examine the mediators and moderators of the SES–ADHD relationship pathway in early childhood.
*UK Millennium Cohort Study (MCS); Alla Barn i Sdöstra Sverige (All Babies in Southeast Sweden, ABIS); Quebec Longitudinal Study of Child Development (QLSCD); Longitudinal Study of Australian Children B cohort (LSAC B); Generation R, Rotterdam, The Netherlands (GenR); National Longitudinal Study of Children and Youth, Canada (NLSCY); and National Longitudinal Study of Youth, USA (US NLSY)
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Organisation for Economic Co-operation and Development (OECD). 2000. Purchasing Power Parities (PPP). Available at: https://data.oecd.org/conversion/purchasing-power-parities-ppp.htm. Accessed May 2022.
Russell AE, Ford T, Williams R, et al. The association between socioeconomic disadvantage and attention deficit/hyperactivity disorder (ADHD): a systematic review. Child Psychiatry Hum Dev 2016; 47: 440-458.
Spencer NJ, Ludvigsson J, Bai G, et al. Social gradients in ADHD by household income and maternal education exposure during early childhood: findings from birth cohort studies across six countries. PLoS One 2022; 17: e0264709.