Modified Overt Aggression Scale (MOAS) for People with Intellectual Disability and Aggressive Challenging Behaviour: A Reliability Study

Background: Reliable measures of aggressive challenging behaviour are required if interventions aimed at reducing this behaviour among people with intellectual disability (ID) are to be formally evaluated. The present authors examined the reliability of the Modified Overt Aggression Scale (MOAS), an instrument not yet formally tested in those with ID, in a sample of people who participated in a randomized trial of neuroleptic medication for aggressive challenging behaviour. Method: Sixty interviews using the MOAS were carried out by two interviewers 2-5 days apart with 23 carers of 14 people who had shown aggressive challenging behaviour. Level of agreement between these two ratings was examined for four subscales of aggression and for total MOAS score. Results: The level of agreement between the raters was high for verbal aggression (intraclass correlation coefficient, ICC = 0.90), physical aggression against others (ICC = 0.90) and for total MOAS score (ICC = 0.93). Levels of agreement on the other two subscales were lower but still in the good/moderate range. Conclusion: The MOAS provides a reliable measure of verbal and physical aggression among people with ID who reside in community settings and is suitable for use in studies evaluating the effectiveness of interventions aimed at reducing aggressive challenging behaviour in this group.