Defining disability in psychosis: performance of the diagnostic interview for psychosis-disability module (DIP-DIS) in the Australian National Survey of Psychotic Disorders

Objective: We aimed to use data from the Australian Survey of Mental Health and Wellbeing to examine the psychometric properties of the Diagnostic Interview for Psychosis-Disability Module (DIP-DIS). The DIP-DIS is a semi-structured questionnaire specially designed to assess disability associated with psychotic disorders. Method: The psychometric properties of the instrument were determined by examining its inter-rater reliability, internal structure, as well as its criterion and discriminant validities. Results: Analysis shows: (1) that it can be rated reliably by trained interviewers, (2) that the items are complementary but tap a number of different domains, (3) that four factors account for over 66% of the variance, and (4) that it is sensitive to differing clinical populations with expected differences in level of disability. Ratings on the DIP-DIS bore significant relationships with a criterion measure of quality of life. Conclusions: The DIP-DIS has encouraging psychometric properties for cross-sectional assessment of disability and may be useful in future studies of disablement associated with psychosis. Future work should examine its sensitivity to change.