Assessing general and autism-relevant quality of life in autistic adults: A psychometric investigation using item response theory.

Although many interventions and services for autistic people have the ultimate goal of improving quality of life (QoL), there is relatively little research on how best to assess this construct in the autistic population, and existing scales designed for non-autistic individuals may not assess all meaningful facets of QoL in the autistic population. To address this need, the autism spectrum QoL form (ASQoL) was recently developed as a measure of the autism-relevant quality of life. However, the psychometrics of the ASQoL have not been examined beyond the authors' initial validation study, and important properties such as measurement invariance/differential item functioning (DIF) have not yet been tested. Using data from 700 autistic adults recruited from the Simons Foundation's SPARK cohort, the current study sought to perform a comprehensive independent psychometric evaluation of the ASQoL using item response theory, comparing its performance to a newly-proposed brief measure of general QoL (the WHOQOL-4). Our models revealed substantial DIF by sex and gender in the ASQoL, which caused ASQoL scores to grossly underestimate the self-reported QoL of autistic women. Based on a comparison of latent variable means, we demonstrated that observed sex/gender differences in manifest ASQoL scores were the result of statistical artifacts, a claim that was further supported by the lack of significant group differences on the sex/gender-invariant WHOQOL-4. Our findings indicate that the ASQoL composite score is psychometrically problematic in its current form, and substantial revisions may be necessary before valid and meaningful inferences can be made regarding autism-relevant aspects of QoL. LAY SUMMARY: Quality of life (QoL) is an extremely important outcome for autistic people, but many of the tools that are used to measure it does not take into account how QoL may be different for autistic people. Using data from 700 autistic adults, we examined the measurement properties of the autism spectrum quality of life form (ASQoL), a new measure of QoL designed specifically for autistic people. Our results indicate that the ASQoL shows a pronounced sex/gender bias, which causes it to underestimate QoL in autistic women. This bias needs to be eliminated before the ASQoL can be successfully used to measure QoL in the autistic population.