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Factor Structure and Longitudinal Measurement Invariance of the Psychopathology in Autism Checklist
Arvid Nikolai Kildahl1,2, Marianne Berg Halvorsen3,4, Jane Margrete Askeland Hellerud5
1Regional Section Mental Health, Intellectual Disabilities/Autism, Oslo University Hospital, Dikemarksveien 39, Asker, 1385, Norway. uxarvk@ous-hf.no.
Journal of Autism and Developmental Disorders
|May 22, 2026
Summary
The Psychopathology in Autism Checklist (PAC) shows promise for screening mental health in autistic adults with intellectual disabilities. An alternative 35-item model demonstrates improved structure and longitudinal invariance for better assessment over time.
Area of Science:
- Psychiatry
- Developmental Psychology
- Clinical Psychology
Background:
- Autistic adults with intellectual disabilities experience high rates of co-occurring mental health conditions.
- Accurate screening tools are crucial for identifying these conditions, especially symptoms distinct from autism.
- The Psychopathology in Autism Checklist (PAC) was developed for this purpose.
Purpose of the Study:
- To examine the factor structure of the Psychopathology in Autism Checklist (PAC).
- To assess the longitudinal measurement invariance of the PAC in autistic adults with intellectual disabilities.
Main Methods:
- Utilized existing data from a longitudinal multicentre study involving autistic individuals with intellectual disabilities.
- Examined PAC factor structure using intake data (N=201).
- Explored longitudinal measurement invariance across three time points (N=173).
Main Results:
- The original PAC subscales showed suboptimal fit; an alternative 35-item model demonstrated improved fit.
- Three original subscales (General Adjustment Problems, Obsessive-Compulsive Disorder, Depression) exhibited longitudinal measurement invariance.
- The alternative model showed improved fit and longitudinal measurement invariance for all five subscales across time points.
Conclusions:
- The findings support further development of the PAC, particularly the alternative 35-item model.
- The alternative model shows enhanced structural validity and suitability for longitudinal comparisons.
- Further research is needed to confirm its utility for screening purposes.
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