The Psychopathology in Autism Checklist-Revised (PAC-R): Development and Validation

There are few appropriate screening tools for mental health in autistic people, particularly for individuals with co-occurring intellectual disabilities. A specially developed screening tool for this population, the Psychopathology in Autism Checklist (PAC), has shown acceptable psychometric properties. However, a recent study showed that the subscale structure of the PAC was not in line with its underlying factor structure. The current study aimed to examine the screening properties of a restructuring of the PAC items in line with its factor structure, resulting in a revised version of the PAC, the PAC-Revised (PAC-R). Cut-offs for the PAC-R subscales were identified in a high-risk sample of autistic adults and older adolescents with intellectual disabilities who had been referred for mental health assessment (n = 182; Sample 1). The psychometric properties of these cut-offs and the statistical fit of the subscales were investigated in this sample, as well as in a low-risk sample of autistic children and adolescents (n = 197; Sample 2). This revised version of the PAC, referred to as the PAC-R and comprising five subscales (obsessive-compulsive disorder, psychosis, anxiety, depression, aggression/self-injurious behaviours) and an "any mental health disorder" index, appeared to retain or improve on the screening properties of the original PAC in Sample 1. Similar findings were made for the anxiety and depression subscales and the "any mental health disorder" index in Sample 2. Statistical fit of the model was acceptable across both samples. These findings indicate that the PAC-R is an applicable mental health screening tool for autistic adults with intellectual disabilities, as well as for anxiety and depression in autistic children and adolescents with varied intellectual functioning.Lay AbstractDespite autistic people being at increased risk of co-occurring mental health disorders, there are few assessment tools developed specifically for the identification of mental health disorders in autistic people. This lack of available tools is especially problematic for autistic individuals with co-occurring intellectual disabilities, who may have difficulties answering questions about potential mental health symptoms, or may display symptoms of mental health disorder in atypical ways. The Psychopathology in Autism Checklist (PAC) has previously been rated as a promising tool for this population. However, a recent finding suggested that the items of the PAC do not seem to be grouping in the way it was presumed when the PAC was first developed. The current study describes the revision of the PAC into the PAC-Revised (PAC-R) and its validation across two different samples. These samples included a high-risk sample for mental health disorder, autistic adults and older adolescents with co-occurring intellectual disabilities referred for mental health assessment, and a lower-risk sample for mental health disorder, autistic children and adolescents referred for initial autism diagnostic assessment. Across both samples, the PAC-R appeared to retain or improve on the properties of the original PAC as a screening tool. In addition, the subscale structure of the PAC-R provided an improved fit to the data with regard to the grouping of the items. In conclusion, the PAC-R appears to be a promising measure for screening for mental health disorders in autistic individuals. However, comprehensive and multimethod assessments remain necessary for making an accurate mental health diagnosis, as the PAC-R is intended for screening purposes only.