Aberrant Behavior Checklist

The ABC is a 58-item caregiver-rated behavioural symptom checklist measuring irritability, social withdrawal, stereotypy, hyperactivity, and inappropriate speech. Used in ASD and intellectual disability clinical trials. Aman et al. (1985).

What is the Aberrant Behavior Checklist?

The Aberrant Behavior Checklist (ABC) is a validated 58-item caregiver-rated scale developed by Aman and colleagues (1985) to assess problem behaviors in individuals with intellectual disabilities. Originally validated in residential settings for adults with ID, the ABC has since been adapted as the ABC-Community (ABC-C) for outpatient and home settings, making it the most widely used behavioural outcome measure in autism spectrum disorder (ASD) clinical trials.

Each of the 58 items is rated on a 4-point scale (0 = not at all a problem, 1 = the behavior is a problem but slight in degree, 2 = the problem is moderately severe, 3 = the problem is severe in degree). Items are summed within each subscale, scores are not averaged.

The ABC Irritability subscale (ABC-I) has served as the primary efficacy endpoint in the pivotal registration trials for both risperidone and aripiprazole — both FDA-approved for the treatment of irritability associated with autism spectrum disorder in children and adolescents. The Marcus et al. (2009) and Owen et al. (2009) aripiprazole trials, and the Pandina et al. (2007) and Kent et al. (2013) risperidone trials, all used ABC-I as the primary outcome measure.

ABC Subscale Reference

Because the ABC produces five independent subscale scores rather than a single total, there are no validated overall severity cutoffs — an automated score interpreter is not applicable for this instrument. Each subscale must be interpreted on its own, in the context of an individual's history and clinical presentation.

Aman et al. (1985) derived the five-factor structure through separate factor analyses of two independent samples totalling over 900 residents with moderate-to-profound intellectual disability. Subscale scores are raw sums. The table below lists each subscale with its item count and maximum possible score.

Common Clinical Trial Thresholds

Across pharmacotherapy trials using the ABC as an outcome measure, two conventions have become standard, though they are not derived from a single defining paper:

Trial entry (eligibility). Pharmacotherapy trials for irritability in autism spectrum disorder have commonly required a minimum ABC-I subscale score at baseline as an eligibility criterion — the exact value varies by trial but is typically in the range of ≥18. This is a commonly used convention representing clinically significant behavioural impairment, not a threshold derived from a single defining psychometric study.

Responder definition. The landmark RUPP Autism Network risperidone trial (McCracken et al., 2002) defined a positive response as at least a 25% decrease in the ABC-I Irritability score plus a rating of "much improved" or "very much improved" on the Clinical Global Impressions-Improvement (CGI-I) scale. This dual criterion — objective symptom reduction plus global clinical impression — was reported in that trial and has since been adopted as a standard convention across multiple subsequent ASD pharmacotherapy trials.

Subscale II (Lethargy/Social Withdrawal). In trials involving individuals with intellectual disability and in some ASD studies, ABC-II is tracked as a secondary endpoint to monitor sedation-related withdrawal as a potential adverse effect of antipsychotic treatment, independent of its role as a symptom subscale.

Behavioural Outcome Tracking in HiBoop

ABC alongside CARS-2, Vineland, and adaptive behavior measures, integrated behavioural outcome monitoring for ASD, ID, and developmental disorder patient panels.