title: Influence of relative age on diagnosis and treatment of attention-deficit/hyperactivity disorder in children.
abstract: BACKGROUND
  The annual cut-off date of birth for entry to school in British Columbia, Canada, is Dec. 31. Thus, children born in December are typically the youngest in their grade. We sought to determine the influence of relative age within a grade on the diagnosis and pharmacologic treatment of attention-deficit/hyperactivity disorder (ADHD) in children.
  
  
  METHODS
  We conducted a cohort study involving 937 943 children in British Columbia who were 6-12 years of age at any time between Dec. 1, 1997, and Nov. 30, 2008. We calculated the absolute and relative risk of receiving a diagnosis of ADHD and of receiving a prescription for a medication used to treat ADHD (i.e., methylphenidate, dextroamphetamine, mixed amphetamine salts or atomoxetine) for children born in December compared with children born in January.
  
  
  RESULTS
  Boys who were born in December were 30% more likely (relative risk [RR] 1.30, 95% confidence interval [CI] 1.23-1.37) to receive a diagnosis of ADHD than boys born in January. Girls born in December were 70% more likely (RR 1.70, 95% CI 1.53-1.88) to receive a diagnosis of ADHD than girls born in January. Similarly, boys were 41% more likely (RR 1.41, 95% CI 1.33-1.50) and girls 77% more likely (RR 1.77, 95% CI 1.57-2.00) to be given a prescription for a medication to treat ADHD if they were born in December than if they were born in January.
  
  
  CONCLUSIONS
  The results of our analyses show a relative-age effect in the diagnosis and treatment of ADHD in children aged 6-12 years in British Columbia. These findings raise concerns about the potential harms of overdiagnosis and overprescribing. These harms include adverse effects on sleep, appetite and growth, in addition to increased risk of cardiovascular events.
authors.affiliation: Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Victoria, BC. richard.morrow@ti.ubc.ca
authors.forename: Richard L
authors.initials: RL
authors.lastname: Morrow
authors.forename: E Jane
authors.initials: EJ
authors.lastname: Garland
authors.forename: James M
authors.initials: JM
authors.lastname: Wright
authors.forename: Malcolm
authors.initials: M
authors.lastname: Maclure
authors.forename: Suzanne
authors.initials: S
authors.lastname: Taylor
authors.forename: Colin R
authors.initials: CR
authors.lastname: Dormuth
mesh_terms: D000367:Age Factors; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000188:drug therapy*; D001955:British Columbia; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D012307:Risk Factors; D012737:Sex Factors