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A Principal Components Analysis of the Autism Diagnostic Interview-Revised

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ABSTRACT

Objective

To develop factors based on the Autism Diagnostic Interview-Revised (ADI-R) that index separate components of the autism phenotype that are genetically relevant and validated against standard measures of the constructs.

Method

ADIs and ADI-Rs of 292 individuals with autism were subjected to a principal components analysis using VARCLUS. The resulting variable clusters were validated against standard measures.

Results

Six clusters of variables emerged: spoken language, social intent, compulsions, developmental milestones, savant skills and sensory aversions. Five of the factors were significantly correlated with the validating measures and had good internal consistency, face validity, and discriminant and construct validity. Most intraclass correlations between siblings were adequate for use in genetic studies.

Conclusion

The ADI-R contains correlated clusters of variables that are valid, genetically relevant, and that can be used in a variety of studies. J. Am. Acad. Child Adolesc. Psychiatry, 2003, 42(7):864-872.

Section snippets

Sample

The principal components analysis used ADIs and ADI-Rs of 292 individuals with autism. Ninety ADIs were from the Baltimore Family Study (Piven et al., 1991, Piven et al., 1994), 107 ADI-Rs were from the New England families of the Collaborative Linkage Study of Autism (CLSA) (e.g., Barrett et al., 1999; CLSA, 2001; Nurmi et al., 2001; and others), and 95 ADI-Rs were purchased from the Autism Genetic Research Exchange (AGRE) database. All cases had a clinical diagnosis of an autism spectrum

Factor Loading and Constructs

Factor I includes a variety of items pertaining to speech behaviors (Table 2). Four of the items in this factor are included in the Communication section in the ADI-R algorithm, but the factor did not include any aspects of language that could be construed as having social communicative intent. Thus we labeled it Spoken Language rather than Communication. Verbal Rituals loaded on this factor, rather than in the Compulsions factor, even though verbal rituals are often compulsive. Its R2 with the

DISCUSSION

In a principal components analysis of items common to the original ADI and its revised version, the ADI-R, six factors were constructed that contain items with good internal consistency and thus form scales, with good face validity, discriminant validity, and construct validity. Our primary goal was to “dissect” the autism phenotype into genetically relevant components. The sib-sib correlations are highly significant for five of the six factors, suggesting that they are appropriate for use in

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    Tadevosyan-Leyfer and Dowd contributed equally to this paper.

    This work was supported by grant MH55135 to Dr. Folstein and PO1DC03610 to Dr. Tager-Flusberg.

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