title: Understanding attention deficit hyperactivity disorder as a continuum.
abstract: OBJECTIVE
  To review research findings that consider whether attention deficit hyperactivity disorder (ADHD) is a discrete entity or whether it is more consistent with an extreme end-of-trait distribution in the population and to then grapple with the potential clinical implications.
  
  
  METHODS
  Peer-reviewed publications in the past 5 years, drawing from diverse fields (taxonomy, epidemiology, genetics, neurobiology, and neuropsychology), were identified through searches in MEDLINE and PsycINFO.
  
  
  RESULTS
  Accumulating research findings are most consistent with a predominately dimensional rather than a qualitatively distinct existence for ADHD. This does not negate the clinical needs of those who have substantial ADHD symptom clusters, nor the risks that such symptoms entail. However, the lack of discontinuity in the distribution of such traits in the population creates great uncertainty as to what thresholds should prompt explicit intervention.
  
  
  CONCLUSIONS
  The implications of this pattern of findings might include the need to de-emphasize categorical conceptualizations of ADHD, produce evidence to better inform risk-benefit ratios of interventions along a spectrum of symptom and functional severity, and more coherently triage and arrange service delivery on the basis of symptom and functional severity rather than artificial diagnostic categorizations.
authors.affiliation: Child psychiatrist at the Children's Hospital of Eastern Ontario in Ottawa, a scientist at the Children's Hospital of Eastern Ontario Research Institute, Research Chair in Child & Adolescent Psychiatry at the University of Ottawa, and Adjunct Associate Professor at the University of Calgary in Alberta. jmclennan@cheo.on.ca.
authors.forename: John D
authors.initials: JD
authors.lastname: McLennan
mesh_terms: D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000628:therapy*; D002648:Child; D039721:Diagnostic and Statistical Manual of Mental Disorders; D006801:Humans; D018570:Risk Assessment