ADHD, comorbid disorders and psychosocial functioning: How representative is a child cohort study? Findings from a national patient registry

Abstract

BackgroundCohort studies often report findings on children with Attention Deficit Hyperactivity Disorder (ADHD) but may be biased by self-selection. The representativeness of cohort studies needs to be investigated to determine whether their findings can be generalised to the general child population. The aim of the present study was to examine the representativeness of child ADHD in the Norwegian Mother and Child Cohort Study (MoBa).MethodsThe study population was children born between January 1, 2000 and December 31, 2008 registered with hyperkinetic disorders (hereafter ADHD) in the Norwegian Patient Registry during the years 2008–2013, and two groups of children with ADHD were identified in: 1. MoBa and 2. The general child population. We used the multiaxial International Classification of Diseases (ICD-10) and compared the proportions of comorbid disorders (axes I–III), abnormal psychosocial situations (axis V) and child global functioning (axis VI) between these two groups. We also compared the relative differences in the multiaxial classifications for boys and girls and for children with/without axis I comorbidity, respectively in these two groups of children with ADHD.ResultsA total of 11 119 children were registered with ADHD, with significantly fewer in MoBa (1.45%) than the general child population (2.11%), p < 0.0001. The proportions of comorbid axis I, II, and III disorders were low, with no significant group differences. Compared with the general child population with ADHD, children with ADHD in MoBa were registered with fewer abnormal psychosocial situations (axis V: t = 7.63, p < .0001; d = -.18) and better child global functioning (axis VI: t = 7.93, p < 0.0001; d = .17). When analysing relative differences in the two groups, essentially the same patterns were found for boys and girls and for children with/without axis I comorbidity.ConclusionsSelf-selection was found to affect the proportions of ADHD, psychosocial adversity and child global functioning in the cohort. However, the differences from the general population were small. This indicates that studies on ADHD and multiaxial classifications in MoBa, as well as other cohort studies with similar self-selection biases, may have reasonable generalisability to the general child population.

Maternal Iodine Intake and Offspring Attention-Deficit/Hyperactivity Disorder: Results from a Large Prospective Cohort Study

“…Another possible explanation might be that there is a tendency that children with both ADHD and more pervasive neurodevelopmental disorders are registered under their primary diagnosis only (e.g., autism) in the NPR. The rate of registered comorbidities to ADHD in the NPR is much lower than would be expected [ 35 ]. This could result in a selection bias for the outcome, potentially also related to our exposure of interest, and thus influence the association that we study.…”

Attention-Deficit/Hyperactivity Disorder in Preschoolers: The Accuracy of a Short Screener

“…50 One study of ADHD in MoBa, reported a lower proportion of ADHD, less psychosocial adversity, and better child global functioning compared to the general child population, but differences were small, and reasonable generalizability to the general child population was assumed. 51 The oversampling for ADHD symptoms at age 3 years gave about a 5-to 8fold increase in the proportion of ADHD compared with preschool prevalence studies, 34,35 and will have increased the probability of finding true cases given a positive screen result. Our sample included children with psychiatric symptoms other than ADHD, such as oppositional defiant disorder (ODD).…”

Adverse family life events during pregnancy and ADHD symptoms in five‐year‐old offspring

“…Selection into the cohort has been shown to influence prevalence estimates for several pregnancy‐related exposures and outcomes, but not the association between these exposures and outcomes (Nilsen et al., ). Findings from a recent study suggest that participants in MoBa are representative for the general population with regard to ADHD, even though participants in MoBa have lower prevalence rates of diagnosed ADHD (Oerbeck et al., ). Participants in MoBa also have higher socioeconomic position than the general population (Magnus et al., ; Nilsen et al., ), and a recent Norwegian study found that families with lower socioeconomic position more frequently experience negative life events (Bøe, Serlachius, Sivertsen, Petrie, & Hysing, ).…”