title: Is the discrepancy criterion for defining developmental disorders valid?
abstract: BACKGROUND
  Most developmental disorders are defined by an achievement discrepancy in which achievement on one or more specific abilities is substantially less than a person's measured intelligence. We evaluated the validity of this discrepancy criterion by assessing parameters that determine variability across abilities and by assessing relationships between achievement discrepancies and behavioral disturbances.
  
  
  METHODS
  Measures of intelligence, language, motor coordination, empathic ability, and attentional control were administered to a representative sample of 390 children aged 3 to 12 years. Parent ratings of child behavior were obtained.
  
  
  RESULTS
  Results indicate that achievement discrepancies are a function of the correlation between ability measures, the shape of the ability distributions, and position on an index ability dimension. Discrepancies in achievement were not related to behavioral disturbance, but underachievement relative to age peers was invariably related to behavioral disturbance.
  
  
  CONCLUSIONS
  We conclude that developmental disorders need to be redefined in ways that are consistent with how Mental Retardation is now defined, by (a) underachievements, (b) of defined magnitude, (c) using standardized measures, (d) with known relations to normal development, and (e) concurrent deficits on standardized measures of impaired function.
authors.affiliation: School of Psychology, Curtin University of Technology, Perth, Australia. m.dyck@curtin.edu.au
authors.forename: Murray J
authors.initials: MJ
authors.lastname: Dyck
authors.forename: David
authors.initials: D
authors.lastname: Hay
authors.forename: Mike
authors.initials: M
authors.lastname: Anderson
authors.forename: Leigh M
authors.initials: LM
authors.lastname: Smith
authors.forename: Jan
authors.initials: J
authors.lastname: Piek
authors.forename: Joachim
authors.initials: J
authors.lastname: Hallmayer
mesh_terms: D000367:Age Factors; D001076:Aptitude; D001288:Attention; D001315:Australia / Q000453:epidemiology; D002648:Child; D002657:Child Development / Q000502:physiology*; D002675:Child, Preschool; D002658:Developmental Disabilities / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007360:Intelligence; D008297:Male; D009048:Motor Skills; D010290:Parents; D011581:Psychological Tests / Q000592:standards* / Q000706:statistics & numerical data; D012737:Sex Factors; D014477:Underachievement