Background. Much of the difficulty in helping the homeless mentally ill arises as a consequence of their resistance to engagement. A refused intervention can seldom influence a client's problems and engagement status can be argued as being an important independent predictor of outcome. No instrument could be identified which systematically measured the factors involved. This paper describes the development and psychometric properties of a new scale, the Homeless Engagement and Acceptance Scale (HEAS).

Method. Staff from an established project for the homeless mentally ill helped to identify relevant questions used to develop a five-item rating scale for completion by an informant. After piloting, the instrument was tested in a study in which subjects were assessed twice over 12 months by informants. Item analysis was undertaken and predictive validity was assessed.

Results. Item analysis indicated a good facility index signifying all items were able to differentiate subjects according to the characteristic being measured, and a high discrimination index demonstrating that all items were measuring the same concept. Predictive validity and internal consistency coefficients were both good. The 3 month HEAS score was found to be a significant predictor of accommodation status and adequacy of a support network at 12 months.

Conclusions. The good psychometric properties and predictive validity of the scale suggest the HEAS is likely to be a useful tool in assessing engagement status. One of the five questions (Q4) can be omitted for those who are not homeless and the scale termed the Engagement and Acceptance Scale (EAS).