Prevalence and risk factors of inpatient aggression by adults with intellectual disabilities and severe challenging behaviour: A long-term prospective study in two Dutch treatment facilities

•Inpatient aggression was recorded in two treatment centres over five years.•On average one aggressive incident per patient per week occurred, including 60% verbal aggression.•About ten times more aggression took place on admission wards compared to resocialisation wards.•Predictors of aggression are aggression early in treatment, low coping skills and impulsiveness.•A method is presented which is suitable for long-term recording of inpatient aggression.

Over five years, various types of aggressive incidents by 421 intellectually disabled inpatients were recorded on a daily basis, using an adapted version of the Modified Overt Aggression Scale. Stable patient characteristics (e.g., gender, intelligence, DSM IV classification at the start of treatment) and pre-treatment scores of two treatment outcome measures (e.g., Adult Behavior Checklist and Dynamic Risk Outcome Scale) were used to predict aggression during the treatment. At an overall average of one incident per patient per week, about ten times more aggression occurred on admission compared to resocialisation wards, and the 20% most aggressive individuals caused 50% of the verbal and 80% of the physical incidents. The best predictor of aggressive behaviour was aggression early in treatment, followed by coping skills deficits and impulsiveness. The relevance of the results for the treatment of aggressive behaviour and methodological issues in the recording of inpatient aggression are discussed.