The Aberrant Behavior Checklist in a Clinical Sample of Autistic Individuals with Intellectual Disabilities and Co-Occurring Mental Health Problems: Psychometric Properties, Factor Structure, and Longitudinal Measurement Invariance.

The Aberrant Behavior Checklist (ABC) was originally developed to evaluate interventions, and is a well-established assessment tool for challenging behaviours in people with intellectual disabilities and autistic people. However, whether the ABC displays longitudinal measurement invariance (i.e., whether it captures the same constructs over time) has been sparsely explored. The aim of the current study is to explore the factor structure, longitudinal measurement invariance, and clinical correlates of the ABC in autistic individuals with intellectual disabilities. Using data from a multicentre study of mental health assessment and treatment in autistic people with intellectual disabilities, the intake ABC scores of 200 autistic individuals with intellectual disabilities were used to explore the ABC factor structure, internal consistency, and clinical correlates (age, gender, level of intellectual disability, autism characteristics, communication skills). Scores across three time points (intake, post-intervention, follow-up) were used to explore longitudinal measurement invariance and internal consistency over time. The original five-factor structure showed a non-optimal but acceptable fit, which was similar or slightly improved compared to previous studies. Associations for some ABC subscales were found to be positive for autism characteristics and negative for communication skills. Four of the five subscales (irritability, social withdrawal, stereotypic behaviour, inappropriate speech) showed residual levels of longitudinal measurement invariance, while one subscale showed noninvariance (hyperactivity/noncompliance). The current study demonstrates the construct validity and applicability of the ABC in autistic individuals with intellectual disabilities, while also indicating that caution is advised for one of its subscales in comparisons across time.