Article

The importance of relative standards in ADHD diagnoses: Evidence based on exact birth dates

Economics Department, Michigan State University, East Lansing, MI 48824-1038, USA.
Journal of Health Economics (Impact Factor: 2.25). 09/2010; 29(5):641-56. DOI: 10.1016/j.jhealeco.2010.06.003
Source: PubMed

ABSTRACT This paper presents evidence that diagnoses of attention-deficit/hyperactivity disorder (ADHD) are driven largely by subjective comparisons across children in the same grade in school. Roughly 8.4 percent of children born in the month prior to their state's cutoff date for kindergarten eligibility - who typically become the youngest and most developmentally immature children within a grade - are diagnosed with ADHD, compared to 5.1 percent of children born in the month immediately afterward. A child's birth date relative to the eligibility cutoff also strongly influences teachers' assessments of whether the child exhibits ADHD symptoms but is only weakly associated with similarly measured parental assessments, suggesting that many diagnoses may be driven by teachers' perceptions of poor behavior among the youngest children in a classroom. These perceptions have long-lasting consequences: the youngest children in fifth and eighth grades are nearly twice as likely as their older classmates to regularly use stimulants prescribed to treat ADHD.

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    ABSTRACT: Background Previous studies from North America and Iceland have shown that the youngest children within a grade are up to twice as likely to be diagnosed and treated for attention-deficit/hyperactivity disorder (ADHD) compared with their older classmates. We aimed to investigate whether younger age in class is associated with an increased probability of being prescribed medication for ADHD among school-aged children in Denmark.Methods We followed all Danish children between 2000 and 2012 from 1st through 6th grade (7–12 years). Among children who started school on their age-assigned grade level, we estimated the prevalence proportion ratio (PPR) of receiving ADHD medication between the youngest children in class (born in October–December) and the oldest in class (born in January–March), specified by grade level, calendar year and gender. As a sensitivity analysis, we added children not on their age-assigned grade level to the main calculations.ResultsWe identified 932,032 eligible children for the main analysis, of whom 17.3% were among the youngest and 26.5% among the oldest in class. In total, 1.2% eligible children filled at least one prescription for ADHD medication in 2000–2012. The average PPR over the study period was 1.08 (95% CI, 1.04–1.12) and remained stable across subgroups and sensitivity analyses. Overall, 40% of children born October–December had entered school a year after their age-assigned grade level.Conclusions Contrary to previous study results, we observed almost no relative age effect on medication use for ADHD among children in Denmark. We postulate that this may be due to the high proportion of relatively young children held back by 1 year in the Danish school system and/or a generally low prevalence of ADHD medication use in the country.
    Journal of Child Psychology and Psychiatry 05/2014; 55(11). DOI:10.1111/jcpp.12243 · 5.67 Impact Factor
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    ABSTRACT: Background We addressed if immaturity relative to peers reflected in birth month increases the likelihood of ADHD diagnosis and treatment.Methods We linked nationwide Patient and Prescribed Drug Registers and used prospective cohort and nested case–control designs to study 6–69 year-old individuals in Sweden from July 2005 to December 2009 (Cohort 1). Cohort 1 included 56,263 individuals diagnosed with ADHD or ever used prescribed ADHD-specific medication. Complementary population-representative cohorts provided DSM-IV ADHD symptom ratings; parent-reported for 10,760 9-year-old twins born 1995–2000 from the CATSS study (Cohort 2) and self-reported for 6,970 adult twins age 20–47 years born 1959–1970 from the STAGE study (Cohort 3). We calculated odds ratios (OR:s) for ADHD across age for individuals born in November/December compared to January/February (Cohort 1). ADHD symptoms in Cohorts 2 and 3 were studied as a function of calendar birth month.ResultsADHD diagnoses and medication treatment were both significantly more common in individuals born in November/December versus January/February; peaking at ages 6 (OR: 1.8; 95% CI: 1.5–2.2) and 7 years (OR: 1.6; 95% CI: 1.3–1.8) in the Patient and Prescribed Drug Registers, respectively. We found no corresponding differences in parent- or self-reported ADHD symptoms by calendar birth month.Conclusion Relative immaturity compared to class mates might contribute to ADHD diagnosis and pharmacotherapy despite absence of parallel findings in reported ADHD symptom loads by relative immaturity. Increased clinical awareness of this phenomenon may be warranted to decrease risk for imprecise diagnostics and treatment. We speculate that flexibility regarding age at school start according to individual maturity could reduce developmentally inappropriate demands on children and improve the precision of ADHD diagnostic practice and pharmacological treatment.
    Journal of Child Psychology and Psychiatry 03/2014; 55(8). DOI:10.1111/jcpp.12229 · 5.67 Impact Factor
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    ABSTRACT: Methylphenidate is a widely prescribed psychostimulant for treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents, which raises questions regarding its potential interference with the developing brain. In the present study we investigated effects of three weeks oral methylphenidate (5 mg/kg) versus vehicle treatment on brain structure and function in adolescent (post-natal day [P]25) and adult (P65) rats. Following a one-week washout period, we used multi-modal magnetic resonance imaging (MRI) to assess effects of age and treatment on Independent Component Analysis (ICA)-based functional connectivity (resting-state functional MRI), D-amphetamine-induced neural activation responses (pharmacological MRI), gray and white matter tissue volumes and cortical thickness (postmortem structural MRI), and white matter structural integrity (postmortem diffusion tensor imaging [DTI]). Many age-related differences were found, including cortical thinning, white matter development, larger dopamine-mediated activation responses, and increased striatal functional connectivity. Methylphenidate reduced anterior cingulate cortical network strength in both adolescents and adults. In contrast to clinical observations from ADHD patient studies, methylphenidate did not increase white matter tissue volume or cortical thickness in rat. Nevertheless, DTI-based fractional anisotropy was higher in the anterior part of the corpus callosum following adolescent treatment. Furthermore, methylphenidate differentially affected adolescents and adults as evidenced by reduced striatal volume and myelination upon adolescent treatment, although we did not observe adverse treatment effects on striatal functional activity. Our findings of small but significant age-dependent effects of psychostimulant treatment in the striatum of healthy rats highlights the importance of further research in children and adolescents that are exposed to methylphenidate.Neuropsychopharmacology accepted article preview online, 15 July 2013. doi:10.1038/npp.2013.169.
    Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 07/2013; 39(2). DOI:10.1038/npp.2013.169 · 7.83 Impact Factor

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