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The Autism Diagnostic Observation Schedule-Generic (ADOS-G) is a semistructured, standardized assessment of social interaction, communication, play, and imaginative use of materials for individuals suspected of having autism spectrum disorders. The observational schedule consists of four 30-minute modules, each designed to be administered to different individuals according to their level of expressive language. Psychometric data are presented for 223 children and adults with Autistic Disorder (autism), Pervasive Developmental Disorder Not Otherwise Specified (PDDNOS) or nonspectrum diagnoses. Within each module, diagnostic groups were equivalent on expressive language level. Results indicate substantial interrater and test-retest reliability for individual items, excellent interrater reliability within domains and excellent internal consistency. Comparisons of means indicated consistent differentiation of autism and PDDNOS from nonspectrum individuals, with some, but less consistent, differentiation of autism from PDDNOS. A priori operationalization of DSM-IV/ICD-10 criteria, factor analyses, and ROC curves were used to generate diagnostic algorithms with thresholds set for autism and broader autism spectrum/PDD. Algorithm sensitivities and specificities for autism and PDDNOS relative to nonspectrum disorders were excellent, with moderate differentiation of autism from PDDNOS.

Word loss is a reliably identifiable phenomenon in early childhood that appears to be unique, but not universal to, ASD. Histories and outcome of children with word loss were not in keeping with a sudden change from normal to abnormal functioning, but did suggest that this type of loss in the second year of life may be a useful 'red flag' for ASD in a significant minority of cases.

The Pre-Linguistic Autism Diagnostic Observation Schedule (PL-ADOS) is a semistructured observation scale designed for use as a diagnostic tool for children less than 6 years old who are not yet using phrase speech and are suspected of having autism. The PL-ADOS takes approximately 30 minutes to administer and is appropriate for use with this population because of its emphasis on playful interactions and the use of toys designed for young children. Reliability studies indicated that both individual activity ratings and summary ratings could be reliably scored from videotaped assessments by naive raters. Additionally, PL-ADOS scores of nonverbal preschool-aged children referred for clinical diagnosis and classified on the basis of a diagnostic team's clinical judgment, clearly discriminated between autistic and nonautistic developmentally disabled children. The resulting diagnostic algorithm is theoretically linked to diagnostic constructs associated with ICD-10 and DSM-IV criteria for autism.

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