Objective: To determine the validity of the Autism-Checklist (ACL) in adults with intellectual disability (ID) who are suspected of having autism spectrum disorder.
Methods: In 154 adults with ID the results of the ACL were compared to the results of the final diagnostic classification obtained by a multiprofessional case conference for autism. Psychometric properties of the ACL were evaluated.
Results: The internal consistency as indicated by Cronbach's alpha was 0.81. The ACL sum score highly correlated with established screening measures such as the Social Communication Questionnaire (SCQ: Spearman's rho = 0.620) and the Pervasive Developmental Disorder in Mental Retardation Scale (PDD-MRS: Spearman's rho = 0.490). ROC Analysis revealed an area under the curve of 0.859. The ACL classification complied with the final diagnostic classification in 80.5 % and Cohen's kappa revealed a moderate agreement of 0.596. Sensitivity/specificity of the ACL were 90.7 %/67.6 %, respectively. Interrater-intertime reliability was good (Cohen's kappa = 0.702; Spearman = 0.549; n = 53). In 19 patients (22 %) a diagnosis of ASD had been given prior to referral.
Conclusion: The ACL is a suitable measure for adults with ID and suspicion of autism spectrum disorders.
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