Examining functional content in widely used Health-Related Quality of Life scales

Assess extent to which generic Quality of Life (QOL) and Health-Related Quality of Life (HRQOL) scales include function in assessment of health, and identify health assessment items that are free of functional content.

An expert panel on measurement of health and disability reached consensus on definitions of health, disability, and function. They assessed all items of all generic (non-condition-specific) scales in the 2006 ProQolid database for being important to measuring health as distinct from function. Ratings were summarized as content validity ratios. Retained items were written into standard format and reviewed again by the expert panel and a validity panel with expertise in specific disabilities.

Of 85 scales, 21 were retained as containing items important for assessing health. Scales ranged from 100% (BRFSS HRQOL, WHO-5) to only 4% of items rated as important. In further review of "important" items, functional content was identified in many of the items, particularly with regard to mental functioning.

Popular generic scales of QOL and HRQOL vary greatly in the degree to which they include content on function. A pool of items can be identified that are relatively free of function. Distinguishing measurement of function and health is particularly important for people with long-standing functional limitations and for assessing the relationship of health with function.