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 the ABC measures

The Aberrant Behavior Checklist (ABC) is a validated 58-item caregiver-rated scale developed by Aman and colleagues (1985) to assess problem behaviours 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 one of the most widely used behavioural outcome measures in autism spectrum disorder (ASD) clinical trials.

It measures five behavioural domains: irritability, lethargy and social withdrawal, stereotypic behaviour, hyperactivity and noncompliance, and inappropriate speech. It does not assess social communication or restricted and repetitive behaviours, so it measures the severity of associated behavioural symptoms rather than the presence of a diagnosis.

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.

How to administer the ABC

The ABC is caregiver-rated, not clinician-administered. A parent, teacher, or other regular caregiver who knows the individual well completes the 58-item checklist based on observations over the past week.

Each of the 58 items is rated on a 4-point scale (0 = not at all a problem, 1 = the behaviour 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.

ABC scoring and interpretation

Because the ABC produces five independent subscale scores rather than a single total, there are no validated overall severity cutoffs — a score interpreter is not applicable for this scale. 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.

Psychometric properties

In the original psychometric study (Aman et al., 1985), internal consistency and test-retest reliability of the checklist were very good. Interrater reliability varied across raters and subscales, ranging from mediocre to good, and was generally in the moderate range and acceptable for research purposes. Validity was supported for most subscales by comparing scores across residents with differing degrees of social adaptation, against adaptive behaviour scales, and against direct behavioural observation.

Limitations

• Not diagnostic. The ABC rates the severity of associated behaviours; it cannot establish or rule out autism or intellectual disability.
• No total score or severity bands. Subscales are interpreted individually, and the trial thresholds above are conventions rather than validated cutoffs.
• Rater dependence. Scores rely on a caregiver's observations over the past week, and interrater agreement in the original study was only moderate.
• Original validation sample. The factor structure was derived in residents with moderate-to-profound intellectual disability; community use relies on the later ABC-Community adaptation.

Measuring Behaviour in HiBoop

HiBoop does not offer the ABC; this page is reference material. HiBoop supports measurement-based care with the scales it offers; see the assessment library.