Gilliam Autism Rating Scale -2

Matthew MeakinSummer 2010

Background Information

Autism is a complex developmental disability that causes problems with social interaction and communication.

Autism Spectrum disorder is a group of different disorders including classic autism, Asperger syndrome, and Pervasive Developmental Disorder.

-The National Institute of Child Health and Human Development www.nichd.nih.gov/health/topics/asd.cfm

Purpose

GARS-2 is a screening tool for autism spectrum disorders for individuals aged 3-22 years old.

GARS-2 was designed to help differentiate between ‘classic’ autism and other spectrum disorders such as Asperger Syndrome and Pervasive Developmental Disorder.

Designed to be used with a variety of diagnostic tools and comprehensive data collection.

(Montgomery, Newton, & Smith 2008)

Utility

GARS-2 relies on caregiver responses (parents & teachers) to obtain information.

42 items divided into three 14-question subscales: Stereotyped Behaviors, Communication, Social Interaction,

Scored on a Likert scale of Never Observed (0) to Frequently Observed (3).

In addition, “Delays In” and “Abnormal Functioning” questionnaire which is scored dichotomously.

Utility - continued

Standard scores are tabulated to yield an Autism Quotient. The AQ has an average of 100 with a standard deviation of 15.

Score Probability of Autism

>69 Very Low

70-79 Low

80-89 Below Ave

90-110 Average

111-120 Above Ave

121-130 High

<130 Very High

Norming Processes

Test manual reports a large normative group. 1107 individuals diagnosed with autism between the ages of 3 and 22 years.

Appropriate percentage representation of race and gender (81% male, 19% female)

(Burros Mental Measurements Yearbooks)

Procedures

Survey is completed by parents, teachers, and a trained professional in an observation setting. Scores are tabulated and referenced.

Reliability

GARS-2 shows good internal consistency for all three subscales and the total score. (Coefficient alphas ranged from .84-.94)

Test-Retest reliability indicated good stability over a one week interval for subscales and Autism Index.

Content Validity

Items measure what the author intends, but there is little evidence to support item identification to individual subscales. For example, subscale items do not correlate exactly to the DSM-IV criteria for Autistic disorders.

Criterion Validity

Scores from GARS-2 and the Autism Behavior Checklist were compared. Significant correlations were found between the two instruments. The Autism Index would appear to be a reliable identifier of autism and autism spectrum disorders.

Administration

The rater can complete the instrument in approximately 10 minutes as long as there is familiarity with the subject.

No specialized training is needed for the caregiver or parent but a trained psychologist or other professional should be used as the third observer.

Test is self-contained. Easy to administer. A lot of information can be obtained in a short

amount of time.

Bias

No particular bias was found, although……..

Strengths & Limitations of the Instrument

Quick, easy, & cheap to administer Construct and content validity are high. Flexibility allows a variety of raters

without modification. Content covers all autism spectrum

disorders Well-standardized, reliable, and valid. The manual is informative and well-

written

Individuals who cannot communicate by language, signs or symbols cannot be scored on the communication subscale.

The age span of 3-22 years may effect diagnosis due to age related development.

Non-professional observations can be more subjective & open to bias.

Instrument is limited in differentiating autism spectrum disorders.

Subscales not clearly linked to DSM-IV definitions of autism.

No clear rationale for item development.

Interrater reliability is not expressly addressed

Probability of autism table is not empirically based.

Commentary

GARS-2 is a well-respected, widely used diagnostic instrument utilized to determine Autism and Autism spectrum disorders in individuals aged 3-22 years old. It has acceptable measures of validity and reliability and appears to be well-normed. The test is easy and to administer while providing accurate feedback.

GARS-2 has added a trained observer section to strengthen the rating system. Whereas teacher feedback is valuable as they spend a great deal of time with the child, it is interesting that equal weight is given to parent feedback. True, parents see their children in non-academic situations but do they have the background knowledge to determine on the Likert scale which behaviors are frequent (for example). Frequent as compared to what? Would seem a relevant question.

Another comment is that autism indicators can be modified through behavior management systems or medicine. Effects of these interventions could lower an indexed score and make symptoms appear more minimal than they are.

References

Eaves, R.C., Woods-Groves, S., Williams, T.O., Jr., & Fall, A-M. (2006) Reliability and validity of the “Pervasive Developmental Disorders Rating Scale” and the “Gilliam Autism Rating Scale.” [Abstract] Education and Training in Developmental Disabilities. 41(3),300- 309. Retrieved from ERIC database.

Fairbank, D.W. & Garro, A. (2007) Test review of Gilliam Autism Spectrum Scale – Second Edition. In Geisinger, K.F., Spies, R.A., Carbon, J.F., & Plake, B.s. (Eds.), The seventeenth mental measurements yearbook [Electronic version]. Retrieved from Academic Search Premier. May 24th, 2010.

Montgomery, J.M., Newton, B., & Smith, C. (2008) Test Reviews: Gilliam, J. (2006). “GARS-2; Gilliam Autism Rating Scale- Second Edition.” Austin, TX: PRO-ED. [Abstract] Journal of Psychological

Assessment. 26(4), 395-401. Retrieved from ERIC database.