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Journal of Autism and Developmental Disorders

Gepubliceerd in:

01-09-2010 | Original Paper

Constructs Assessed by the GARS-2: Factor Analysis of Data from the Standardization Sample

Auteurs: Vincent Pandolfi, Caroline I. Magyar, Charles A. Dill

Gepubliceerd in: Journal of Autism and Developmental Disorders | Uitgave 9/2010

Abstract

The GARS-2 (Gilliam 2006) is widely used for autism screening; however, the validity of its three conceptually-derived subscales has not been evaluated. In this study, exploratory (EFA) and confirmatory (CFA) factor analyses of data from matched subgroups of the standardization sample did not support the GARS-2 subscale structure. EFAs identified four factors in the model development subgroup (n = 496): stereotyped/repetitive behavior, stereotyped/idiosyncratic language, word use problems, and social impairment. CFAs supported this model in the replication subgroup (n = 494). Findings suggest that the GARS-2 subscales have limited clinical utility and that the Autism Index should be interpreted with caution. Although more research is needed, the clinical utility of the four empirically-derived scales may be limited by factors related to item content and test development procedures.

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Throughout this paper “autism” refers to DSM-IV-TR Autistic Disorder.

Level 1 screening discriminates those at risk for a developmental disorder from typically developing children. Level 2 screening discriminates those at risk for autism from those with other developmental disorders.

The Communication subscale is not administered to nonverbal individuals. The Autism Index is based on the Stereotyped Behavior and Social Interaction subscale standard scores.

Including all subjects would essentially result in a pairwise deletion of missing data in the analyses, and item correlations for factor analyses would be based on unequal sample sizes. Problems with this approach are discussed in Brown (2006).

The different sample size was an artifact of the random assignment procedure. An odd number of participants comprised some age-level groupings, and random assignment more often placed a final subject in the EFA group.

A total of 34 zero frequency cells were observed in the EFA dataset and 39 in the CFA dataset. This represented 0.25 and 0.28% of all cells in the EFA and CFA datasets, respectively. Since this was unlikely to significantly affect results, it was not necessary to delete items or collapse Likert categories.

These results are available upon request from the first author.

Factor pattern coefficients not presented to conserve space but are available upon request from the first author.

Post-hoc invariance tests did not support tau equivalence for items within any factor. This means that items within the same scale measure different amounts of true score variance in their latent factor. Thus a congeneric model was accepted.

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Titel: Constructs Assessed by the GARS-2: Factor Analysis of Data from the Standardization Sample
Auteurs: Vincent Pandolfi
Caroline I. Magyar
Charles A. Dill
Publicatiedatum: 01-09-2010
Uitgeverij: Springer US
Gepubliceerd in: Journal of Autism and Developmental Disorders / Uitgave 9/2010
Print ISSN: 0162-3257
Elektronisch ISSN: 1573-3432
DOI: https://doi.org/10.1007/s10803-010-0967-1

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