Validity of the Capacity to Work Index: Development of an Instrument to Measure Work Capacity in Relation to Depression and Anxiety in the General Working Population.

Purpose: To develop an index to assess capacity to work in relation to common mental disorders (CMDs) in the general working population and field test its psychometric properties.

Methods: Content analysis of three qualitative studies on people (n = 49) with their own experiences of working with CMD guided the items selected for the index. Face and content validity and test-retest reliability were performed. The index was field tested in two versions with 26 and 17 items, respectively, among health care professionals regarding internal reliability, component structure and concurrent validity.

Results: The final version of the Capacity to Work Index (C2WI; 17 items) was normally distributed in the field test with high internal reliability (Cronbach's alpha, 0.84). Missing responses were randomly distributed and nonspecific. Principal component analysis showed one clear component with negatively framed items. Concurrent validity showed high correlation with the WHO-5 Well-Being Scale (Pearson's r, 0.68), but lower correlation for the general health question (r, - 0.44), one item of the Work Ability Index (r, - 0.33), and the Stress of Conscience constructs (r, 0.44).

Conclusion: The C2WI showed promising psychometric qualities. Low and negative correlation with the item from Work Ability Index suggests that the C2WI measures additional dimensions, but further testing in larger and more diverse samples is required.