Studies that compared English language screening or diagnostic tools with a reference standard based on the American Psychiatric Association's DSM-III/IV criteria or International Classification of Diseases (ICD 10) criteria for diagnosing autism or autistic spectrum disorder, and that were conducted in children aged younger than four years at screening with no prior diagnosis of developmental delay, were eligible for inclusion. The screening tools had to be appropriate for use in a general primary care setting (ability to score the tool in a brief consultation without extensive prior training). Studies that assessed only Asperger's Syndrome were excluded, as were studies that assessed global development delay.
The included studies were diagnostic cohort studies that assessed the Checklist for Autism in Toddlers (CHAT; parent and professional report) and modified CHAT (M-CHAT; parent report only) screening tools. These tools require minimal training and take approximately 15 minutes to complete. Screening was performed by general practitioners, health professionals or parents. The reference standards used by the included studies were DSM-III, DSM-IV and ICD-10 criteria. Diagnosis was made after between 1 and 5.5 years' follow-up. The included children were aged from 17 to 24 months. The outcomes reported in the review were the sensitivity, specificity, and positive and negative predictive values.
One reviewer selected studies for inclusion and a second reviewer checked the decision.