title: Quantitative autistic traits ascertained in a national survey of 22 529 Japanese schoolchildren.
abstract: OBJECTIVE
  Recent epidemiologic studies worldwide have documented a rise in prevalence rates for autism spectrum disorders (ASD). Broadening of diagnostic criteria for ASD may be a major contributor to the rise in prevalence, particularly if superimposed on an underlying continuous distribution of autistic traits. This study sought to determine the nature of the population distribution of autistic traits using a quantitative trait measure in a large national population sample of children.
  
  
  METHODS
  The Japanese version of the Social Responsiveness Scale (SRS) was completed by parents on a nationally representative sample of 22 529 children, age 6-15.
  
  
  RESULTS
  Social Responsiveness Scale scores exhibited a skewed normal distribution in the Japanese population with a single-factor structure and no significant relation to IQ within the normal intellectual range. There was no evidence of a natural 'cutoff' that would differentiate populations of categorically affected children from unaffected children.
  
  
  CONCLUSIONS
  This study provides evidence of the continuous nature of autistic symptoms measured by the SRS, a validated quantitative trait measure. The findings reveal how paradigms for diagnosis that rest on arbitrarily imposed categorical cutoffs can result in substantial variation in prevalence estimation, especially when measurements used for case assignment are not standardized for a given population.
authors.affiliation: Department of Child and Adolescent Mental Health, National Institute of Mental Health, National Center of Neurology and Psychiatry, Tokyo, Japan. kamio@ncnp.go.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Kamio
authors.forename: N
authors.initials: N
authors.lastname: Inada
authors.forename: A
authors.initials: A
authors.lastname: Moriwaki
authors.forename: M
authors.initials: M
authors.lastname: Kuroda
authors.forename: T
authors.initials: T
authors.lastname: Koyama
authors.forename: H
authors.initials: H
authors.lastname: Tsujii
authors.forename: Y
authors.initials: Y
authors.lastname: Kawakubo
authors.forename: H
authors.initials: H
authors.lastname: Kuwabara
authors.forename: K J
authors.initials: KJ
authors.lastname: Tsuchiya
authors.forename: Y
authors.initials: Y
authors.lastname: Uno
authors.forename: J N
authors.initials: JN
authors.lastname: Constantino
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D017677:Age Distribution; D001321:Autistic Disorder / Q000175:diagnosis* / Q000453:epidemiology*; D002648:Child; D002652:Child Behavior / Q000523:psychology*; D002657:Child Development; D005260:Female; D006801:Humans; D007398:Interpersonal Relations; D007564:Japan / Q000453:epidemiology; D008297:Male; D008403:Mass Screening / Q000706:statistics & numerical data; D010379:Peer Group; D010551:Personality; D011569:Psychiatric Status Rating Scales; D011594:Psychometrics; D012307:Risk Factors; D017678:Sex Distribution; D012919:Social Behavior