The Gilliam Autism Rating Scale (GARS) helps to identify and diagnose autism in individuals ages 3 through 22 and to estimate the severity of the problem. Items on the GARS are based on the definitions of autism adopted by the Autism Society of America and the Diagnostic and Statistical Manual of Mental Disorders: Fourth Edition (DSM­-IV).

The items are grouped into four subtests:

• Stereotyped Behaviours

• Communication 

• Social Interaction 

• Developmental Disturbances. 

The GARS has three core subtests that describe specific and measurable behaviours and an optional subtest (Developmental Disturbances) that allows parents to contribute data about their child’s development during the first 3 years of life.

The GARS has strong psychometric characteristics that were confirmed through studies of the test’s reliability and validity. Coefficients of reliability (internal consistency, test­ retest, and interscorer) for the subtests are all in the .80s and .90s. The GARS is the only test for autism that reports data for all three kinds of reliability. The validity of the GARS was demonstrated by confirming that: (a) the items of the subtests are representative of the characteristics of autism; (b) the subtests are strongly related to each other and to performance on other tests that screen for autism; and (c) the GARS performance discriminates persons with autism from persons with other severe behavioural disorders such as emotional disturbance, speech and language disorders and other multidisabling conditions.

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