 Development and Content Validation of the IMPAC Scale 
The IMPAC Scale (Impact des problèmes actuels de comportement) is an instrument designed to evaluate the impact of challenging behaviour in people with acquired brain injury. This scale measures the impact of such behaviour on the brain-injured person and their social network based on five areas: significant relationships, psychological integrity, access to services, physical integrity and received interventions. The instrument was initially developed by specialized practitioners working with brain-injured persons exhibiting severe challenging behaviour. A series of three validation studies were conducted in which experts and practitioners in fields such as acquired brain injury rehabilitation were consulted. The results showed that the IMPAC Scale has satisfactory content validity — i.e. targeted impact areas and described impact levels are based on clearly defined criteria recognized as such by experts and practitioners. Therefore, the IMPAC Scale can be a useful tool for clinicians who need to objectively assess the impact of a user’s challenging behaviour, which can help prioritize interventions and recommend appropriate residential facilities or specialized services.