title: A screening instrument for autism at 18 months of age: a 6-year follow-up study.
abstract: OBJECTIVE
  A population of 16,235 children aged 18 months was screened using the Checklist for Autism in Toddlers (CHAT) to identify childhood autism (CA). Two further screening procedures were conducted at age 3 and 5 years. The population was followed up at age 7 years in order to establish the sensitivity, specificity, and positive predictive value of the instrument.
  
  
  METHODS
  A brief checklist assessing joint attention and pretend play behaviors was administered by primary health care practitioners when the children were 18 months old. Follow-up methods included screening through parents and health practitioners and checking medical and educational records.
  
  
  RESULTS
  Nineteen cases of CA were successfully identified by the CHAT at 18 months. At follow-up a total of 50 cases of CA were identified via all surveillance methods. Thus, the CHAT has a sensitivity of 38% and a specificity of 98% for identifying CA. The positive predictive value of the instrument was maximized by concentration on the highest-risk group. Repeated screening 1 month later increased the positive predictive value to 75% for identification of CA but reduced the sensitivity to 20%, although the specificity was close to 100%. The screen also identified cases of pervasive developmental disorder as well as children with language and other developmental disorders.
  
  
  CONCLUSIONS
  The CHAT can be used to identify cases of autism and related pervasive developmental disorders at 18 months of age. It is emphasized that the CHAT is not a diagnostic instrument but can identify potential cases of autism spectrum disorders for a full diagnostic assessment.
authors.affiliation: Newcomen Centre, Guy's Hospital, London.
authors.forename: G
authors.initials: G
authors.lastname: Baird
authors.forename: T
authors.initials: T
authors.lastname: Charman
authors.forename: S
authors.initials: S
authors.lastname: Baron-Cohen
authors.forename: A
authors.initials: A
authors.lastname: Cox
authors.forename: J
authors.initials: J
authors.lastname: Swettenham
authors.forename: S
authors.initials: S
authors.lastname: Wheelwright
authors.forename: A
authors.initials: A
authors.lastname: Drew
mesh_terms: D001321:Autistic Disorder / Q000175:diagnosis* / Q000453:epidemiology; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis; D002675:Child, Preschool; D015986:Confounding Factors, Epidemiologic; D002658:Developmental Disabilities / Q000175:diagnosis; D003937:Diagnosis, Differential; D004739:England / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D008297:Male; D008403:Mass Screening / Q000379:methods*; D011159:Population Surveillance; D011237:Predictive Value of Tests; D015995:Prevalence; D011569:Psychiatric Status Rating Scales / Q000592:standards*; D012680:Sensitivity and Specificity