CHAT
Contents
CHAT
Basic Characteristics
- Description
The CHAT was designed to be administered by a general practioner or health visitor at 18 months of age as a screening tool for childhood autism. The test measures pretend play, protodeclarative pointing, and gaze monitoring using general practicioner and parent observations. However, the CHAT was not designed to be a diagnostic tool-more than half the children who fail the first administration pass the second time. Thus children who fail twice should be referred to a specialist for a thorough diagnosis.
The tool is composed of two sections. Section A consists of 9 yes/no questions which takes 5-10 minutes to answer and is easy to score. Section B is composed of 5 items which are completed by the general practioner as he/she observes the child. Five key items relating to joint attention and pretend play for Section B help validate parent answers in section A. The rest of the items in section B are meant to provide additional information to distinguish autism from global developmental delays.
The scoring criteria stratifies children into high, medium, and low risk groups for autism. If a child meets the criteria for a high risk group, he/she will most likely be diagnosed with autism or PDD through an actual diagnostic test. About half of the medium risk group will be diagnosed with autism or PDD and the other half will likely have other developmental delays. 1
- History
Scoring
"Failure" of the CHAT consists of "failing" on both sections A and B.
Key items are 5 and 7 and section A and ii, iii, and iv in section B. A "No" answer for all of these key items are at high risk for autism. Those who fail both items that measure protodeclarative pointing (Section A, Question 7 and Section B Question iv) but are not in the high risk group are at medium risk for autism.
Those who fall in neither autism profiles are deemed as low risk. 1
Psychometrics (validity and reliability)
The CHAT has an overall sensitivity of 38% and specificity of 98% for childhood autism. Repeating the screening 1 month after the initial screening gives a PPV=98%, but reduced the sensitivity to 20%, though specificity was close to 100%.
The CHAT has a sensitivity of 18%, specificity of 100%, positive predictive value of 75% and negative predictive value of 99.7% for the high risk criteria. For all PPDs, the medium and high risk criteria had a sensitivity of 21.3%, specificity of 99.9%, and positive predictive values of 58.8%.1
References
1. Baron-Cohen, S. et. al. Early identification of autism by the CHecklist for Autism in Toddlers (CHAT).J R Soc Med. 2000 Oct;93(10):521-5 PMID 11064690
