Psychometric properties of the Psychopathology in Autism Checklist (PAC)

Abstract

Psychiatric disorders in individuals with co-occurring autism spectrum disorders (ASD) and intellectual disability (ID) are common, but diagnosis presents many challenges. The Psychopathology in Autism checklist (PAC) is among the very few instruments specifically developed for this group of individuals. The psychometric properties of the PAC (i.e. criterion validity, specificity, sensitivity and predictive values) were explored by comparing scores with assessments on the Aberrant Behavior Checklist (ABC) and examining how well assessment by the PAC at referral predicts final clinical diagnoses. Results indicated a significant correlation with the ABC, further supporting the validity of the PAC. Sensitivity and Specificity for specific diagnoses were variable, although positive predictive value for "any diagnosis' was relatively high. The study confirms the potential value of the PAC as a screening checklist but highlights the need for clinical diagnosis to be based on a multimodal, multidisciplinary assessment.

Schizophrenia in autistic people with intellectual disabilities: Symptom manifestations and identification

“…While statistically significant differences between the groups were found for PAC psychosis across the analyses, sensitivity (.62) and specificity (.69) for schizophrenia in the current sample were acceptable to poor. This is in line with previous findings from a partially overlapping sample, where sensitivity and specificity of PAC psychosis for schizophrenia were .65 and .62 (Helverschou, Ludvigsen, et al, 2021). However, psychotic symptoms are not specific to schizophrenia and may occur in other mental disorders, such as affective disorders (APA, 2013; WHO, 1992), and the PAC psychosis scale is unlikely to be specific to schizophrenic psychoses.…”

“…The psychosis scale of the PAC seemed to differentiate participants diagnosed with schizophrenia from both comparison groups. This is in line with a previous study comparing three similar groups, of which one was comprised of autistic individuals with intellectual disabilities and psychosis (Bakken et al, 2007), and previous studies on the PAC (Helverschou et al, 2009; Helverschou, Ludvigsen, et al, 2021). However, the PAC psychosis scale was the only PAC/ABC scale that differentiated the group with schizophrenia from the group with other mental disorders in this study.…”

“…The PAC (Helverschou et al, 2008, 2009) is a caregiver‐completed mental disorder screening checklist developed for autistic individuals with intellectual disabilities. Psychometric properties of the PAC have been found to be acceptable to good (Helverschou et al, 2008, 2009; Helverschou, Ludvigsen, et al, 2021). It has been found to distinguish reliably between mental health symptoms and the core characteristics of ASD (Helverschou et al, 2008), to distinguish autistic adults with intellectual disabilities and co‐occurring mental disorder from those without mental disorder (Bakken et al, 2010; Helverschou et al, 2009; Helverschou, Ludvigsen, et al, 2021), and to a certain extent to distinguish between individuals with different mental disorders (Dalhaug et al, 2022; Helverschou et al, 2009; Helverschou, Ludvigsen, et al, 2021).…”

“…The PAC comprises 42 items distributed across five scales; psychosis (10 items), depression (7 items), anxiety disorders (6 items), OCD (7 items), and general adjustment problems (GAP; 12 items). Each item is rated in two domains: “Extent of problems” (not a problem = 1, minor problem = 2, moderate problem = 3, severe problem = 4) and “Change from usual behaviour” (worsened, unchanged, improved; see Helverschou, Ludvigsen, et al, 2021; Helverschou et al, 2008, 2009). A two‐step procedure identifies individuals with a possible mental disorder.…”

“…When the very few missing values were treated as “not a problem”, overall internal consistency of the PAC was good in this sample (Cronbach's α = .90), as well as for PAC psychosis ( α = .77), PAC depression ( α = .77), PAC anxiety ( α = .70), PAC OCD ( α = .75), and PAC general adjustment difficulties ( α = .70). The study by Helverschou, Ludvigsen, et al (2021) has explored the psychometric properties of the PAC using data from the AUP study, including sensitivity/specificity of the scales, with a partly overlapping sample to the current study.…”