Wednesday, March 16, 2011

Test Review: The Gilliam Autism Rating Scale: Second Edition (GARS-2)

The GARS-2 is a revision of the widely used Gilliam Autism Rating Scale (1995). It was designed to assist psychologists, teachers, parents, and clinicians in identifying and diagnosing autism in individuals aged 3 through 22 and in estimating the severity of the disorder. The GARS-2 can be individually administered in 5 to 10 minutes and consists of 42 items describing the characteristic behaviors of persons with autism. The items are grouped into three subscales based on two definitions of autism, one from the Autism Society of America and the other from the diagnostic criteria for autistic disorder published in the DSM-IV-TR (American Psychiatric Association, 2000):
  • Stereotyped Behaviors
  • Communication
  • Social Interaction 
The subscale standard scores are summed to produce an Autism Index (mean = 100, SD = 15). Higher standard scores and Autism Indices are indicative of more problematic behavior. Scoring also includes a Probability of Autism classification (Very Likely, Possibly, Unlikely). 

According to the test manual, the second edition reflects several positive changes such as: (a) updated, more clearly described norms; (b) rewriting of some items and the scoring guidelines to improve clarity; and (c) a section that provides specific item definitions and examples for applied behavior analysis and research projects. New to the second edition is a structured interview form for gathering diagnostically important information from the child's parents that replaces the Early Development subscale found in the original version. The GARS-2 was normed on a representative sample of 1,107 persons with autism from 48 states within the United States. Demographic characteristics of the normative sample are keyed to the 2000 U.S. Census data. Few changes were made to GARS test items in developing the GARS-2. The difference between versions exists mostly on the fourth subscale, labeled ‘Developmental Disturbance’ on the GARS and ‘Parent Interview’ on the GARS-2.

Independent studies on the first version of the instrument have indicated less than optimal psychometric properties. For example, research examining the validity of the GARS (1995) consistently found that the scale underestimated the likelihood of children with autism being classified as having autism, indicating low sensitivity, with values ranging from .38 to .53 (Norris and Lecavalier, 2010). Sensitivity is the percentage of true cases correctly identified by a screen; a sensitivity value of .80 is the accepted standard.

A recent study of the validity of the GARS-2 three subscales did not support the subscale structure (Pandolfi, Magyar, & Dill, 2010). The findings suggest that the clinical utility of the scales is limited by factors related to item content and test development procedures and that the Autism Index be interpreted with caution. The Probability of Autism classification also lacks a sound empirical basis and may be subject to misinterpretation. A previous review also notes that although the names of the subscales correspond to the main DSM-IV criteria for Autistic Disorder, the items do not correspond entirely to the behavioral characteristics listed under these criteria or to the traits listed on the website of the Autism Society of America (Garro, 2006). 

There are also questions regarding the normative sample (Norris & Lecavalier, 2010). Group membership was determined via caregiver report of diagnosis and/or school classification. A number of participants (27%) were recruited from the Asperger Syndrome Information and Support website, suggesting that a portion of the sample may have included individuals with other pervasive developmental disorders (PDD/ASD). Although the sample participants should have been diagnosed with autism, there is no information about the specific diagnostic criteria that were in fact used. Diagnosis of participants was not confirmed by the ADI-R, ADOS, or a clinical evaluation. Although the norms are not based upon age, the underrepresentation of older children and young adults also suggests that practitioners need to use caution when using the instrument with individuals from these age groups (Garro, 2006). From a more positive perspective, there is some preliminary support for the validity of the broad-based Autism Index. The content of the GARS-2 also reflects a number of behavioral characteristics that apply to individuals with ASD and may help guide the user in understanding the “autistic triad.” The manual also includes several cautions for the interpretation of results.

According to the manual, the GARS-2 should be administered by professionals who have training and experience in working with individuals with autism such as school psychologists, educational diagnosticians, and autism specialists. Practitioners who are currently using or considering using the GARS/GARS-2 for making an autism diagnosis or assessing symptom severity should exercise caution due to significant weaknesses, including the underidentification of higherfunctioning ASD and questions concerning standardization and norming procedures. Although the GARS-2 may have utility as a general screening or supplementary tool for ASD, it is not recommended it for inclusion as the primary phenotypic instrument in a comprehensive developmental assessment battery for autism (Norris & Lecavalier, 2010; Wilkinson, 2010). 

Garro, A. (2006). Review of the Gilliam Autism Rating Scale-Second Edition. Seventeenth mental measurements yearbook with Tests in Print, Buros Institute of Mental Measurement. Lincoln: University of Nebraska Press.

Gilliam, J. (2006). GARS-2: Gilliam Autism Rating Scale-Second Edition. Austin, TX: PRO-ED.

Lecavalier L. (2005). An evaluation of the Gilliam Autism Rating Scale. Journal of Autism and Developmental Disorders, 35, 795-805.

Norris, M., & Lecavalier, L. (2010). Screening accuracy of level 2 autism spectrum disorder rating scales: A review of selected instruments. Autism, 14, 263-284.

Pandolfi V., Magyar C. I., & Dill C. A. (2010). Constructs assessed by the GARS-2: factor analysis of data from the standardization sample. Journal of Autism & Developmental Disorders, 40, 1118-30. 

Wilkinson, L. A. (2016). A best practice guide to assessment and intervention for autism spectrum disorder in schools. London: Jessica Kingsley Publishers.

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