Background: The autism spectrum (AS) is a multifaceted neurodevelopmental variant associated with lifelong challenges. Despite the relevant importance of identifying AS in adults for epidemiological, public health, and quality of life issues, the measurement properties of the tools currently used to screen and diagnose adults without intellectual disabilities (ID) have not been assessed.
Objectives: This systematic review addresses the accuracy, reliability, and validity of the reported AS screening and diagnostic tools used in adults without ID.
Methods: Electronic databases and bibliographies were searched, and identified papers evaluated against inclusion criteria. The PRISMA statement was used for reporting the review. We evaluated the quality of the papers using the COSMIN Checklist for psychometric data, and QUADAS-2 for diagnostic data. For the COSMIN assessment, evidence was considered to be strong when several methodologically good articles, or one excellent article, reported consistent evidence for or against a measurement property. For the QUADAS ratings, evidence was considered to be "satisfactory" if at least one study was rated with a low risk of bias and low concern about applicability.
Results: We included 38 articles comprising 32 studies, five reviews, and one book chapter and assessed nine tools (three diagnostic and six screening, including eight of their short versions). Among screening tools, only AQ-50, AQ-S, and RAADS-R and RAADS-14 were found to provide satisfactory or intermediate values for their psychometric properties, supported by strong or moderate evidence. Nevertheless, risks of bias and concerns on the applicability of these tools limit the evidence on their diagnostic properties. We found that none of the gold standard diagnostic tools used for children had satisfactory measurement properties.
Conclusion: There is limited evidence for the measurement properties of the screening and diagnostic tools used for AS adults with a mean normal range of measured intelligence. This may lessen the validity of conclusions and public health decisions on an important fraction of the adult autistic population. This not only justifies further validation studies of screening and diagnostic tools for autistic adults, but also supports the parallel use of self-reported information and clinical expertise with these instruments during the diagnostic process.
Keywords: Autism; Diagnosis; Screening; Systematic review.
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