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What is the Gilliam Autism Rating Scale?

September 22, 2023

The journey to attaining a diagnosis of autism spectrum disorder (ASD) often comes with many hurdles and back-and-forth consultations. Some parents only receive a positive diagnosis after years of seeking answers for their children’s challenges, but tools such as the Gilliam Autism Rating Scale are designed to help. 

What is the Gilliam Autism Rating Scale?

Due to the spectrum of autism, diagnostic instruments have been developed to help clinicians or examiners measure traits against specific test items. These items are specific based on autism criteria, and scores are obtained to determine the degree of difficulty for each individual child and where on the spectrum the child may best fit (i.e. high-functioning or low-functioning autism). 

The Gilliam Autism Rating Scale-Third Edition, also known as the GARS-3, aims to aid parents, clinicians and teachers in determining the severity of autism within different individuals.  

Why was the Gilliam Autism Rating Scale created?

Autism exists on a spectrum whereby the degree of difficulties differ across every individual. Because of the continuum of autism, diagnosis can be challenging as some children do not tick all the boxes. For this reason, various subtypes of autism were established by medical professionals, one of which was Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS), and another being asperger’s syndrome.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) now groups most of these subtypes under the umbrella category of autism spectrum disorder (ASD), but a diagnosis of PDD-NOS is given when children show signs of autism but don’t necessarily meet all the criteria.

In clinical practice, the diagnosis of ASD tends to rely on standardized diagnostic measures, along with clinical judgement with little backup from diagnostic instruments. Therefore, the lack of clarity in diagnosis led to the creation of autism scales such as the GARS-3 scale.

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Elements of the Gilliam Autism Rating Scale

The Gilliam Autism Rating Scale was developed by James E. Gilliam, and the Third Edition of the manual was published in 2013. The GARS-3 reflects the items and subscales of the DSM-5. It is designed to screen for ASD in people aged between three and 22 years. 

A key feature of the GARS-3 is that it is a norm-reference tool, meaning the test compares and ranks scores based on the individuals in the same group (norm group). A norm group could be categorized based on age, socioeconomic status, race/ethnicity etc. depending on the specific test.

The kits of the GARS-3

  • An Examiner’s Manual
    • Contains the procedure to administer the test, scoring procedure, and technical information 
  • Summary/response forms
    • Completed by the examiner and includes information about the examinee’s demographic information, responses to the items on the scale, and important information for diagnosing ASD
  • The Instructional Objectives for Individuals Who Have Autism booklet
    • Helps parents and professionals develop instructional goals and behavioral interventions based on the findings of the diagnostic instrument

Subscales of the GARS-3

The GARS-3 has six different subscales that were developed according to the DSM-5 and the American Psychiatric Association (APA) definitions of autism spectrum disorder.

The subscales include: 

  • Restricted/Repetitive Behaviors (13 items)
  • Social Interaction (14 items)
  • Social Communication (9 items)
  • Emotional Responses (8 items)
  • Cognitive Style (7 items)
  • Maladaptive Speech (7 items)

Summing up

The Third Edition of the GARS is shorter and easier to administer than its predecessor. Evidence from researchers and testers has indicated that its scores are valid and reliable. In addition, it is in line with the Autism Society’s definition of autism as well as the DSM-5.

The main limitation of the GARS scale is that it can only be compared against individuals diagnosed with autism. In addition, the normative sample collected on the scale is mainly composed of White or Black/African races between the age of three and 19 years; this limitation questions suitability for other races and ethnicities and those between the ages of 20 to 22 years and those younger than three.


Chlebowski, C., Green, J. A., Barton, M. L., & Fein, D. (2010). Using the childhood autism rating scale to diagnose autism spectrum disorders. Journal of autism and developmental disorders, 40(7), 787–799. https://doi.org/10.1007/s10803-009-0926-x

Karren, B. C. (2017). A Test Review: Gilliam, J. E. (2014). Gilliam Autism Rating Scale–Third Edition (GARS-3). Journal of Psychoeducational Assessment, 35(3), 342–346. https://doi.org/10.1177/0734282916635465

Lecavalier, L. (2005). An Evaluation of the Gilliam Autism Rating Scale. Journal of Autism and Developmental Disorders, 35, 795, https://doi.org/10.1007/s10803-005-0025-6


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