Objectives: To investigate the ideal CARS cutoff for a diagnosis of Autistic Disorder and to investigate the utility of the CARS as a tool for ASD diagnoses in samples of 2-year-old and 4-year-old children referred for possible autism.
Methods: Participants were 376 two-year-old and 230 four-year-old children who were screened with the M-CHAT (Robins, et al., 2001), and evaluated at age 2 (mean age=26 months) and/or age 4 (mean age=54 months) using the ADI-R, ADOS, and the CARS, and were given diagnoses from clinical judgment based on DSM-IV criteria. Sensitivity, specificity, and positive and negative predictive values were calculated to determine optimal CARS cutoff scores for a diagnosis of Autistic Disorder as well as for an ASD diagnosis as compared to a gold standard diagnosis based on clinical judgment.
Results: Consistent with Lord (1995), the optimal cut-off score to distinguish Autistic Disorder from PDD-NOS in the two-year-old sample was 32, with a sensitivity (relative to Clinical Best Estimate diagnosis) of 0.79 and a specificity of .81. The optimal cut-off score to distinguish Autistic Disorder from PDD-NOS in the four-year-old sample was 30 with sensitivity of .86 and a specificity of .80. The optimal cut-off score to distinguish ASD from non-ASD in both samples was 25.5, with a sensitivity of .92 and a specificity of .89 in the two-year-old sample and a sensitivity of .82 and a specificity of .95 in the four-year-old sample.
Conclusions: Results suggest that, in a two-year-old sample, a cutoff of score of 32 more accurately distinguishes Autistic Disorder from PDD-NOS than the current cutoff of 30. Findings confirm the utility of the CARS in distinguishing Autistic Disorder from PDD-NOS, and distinguishing ASD from other developmental disorders and typical development and suggest that an ASD cutoff around 25, which is in common clinical use, is valid.