Development and psychometric properties of a “function-neutral” measure of health-related quality of life

Background: Measures of health-related quality of life (HRQOL) often include assessment of functional abilities, resulting in lower HRQOL scores for people with functional limitations. The conceptual confusion of health and function limits the usefulness of many HRQOL measures with persons with pre-existing functional limitations or disabilities. This presentation will describe a new generic measure of HRQOL that is designed to be function-neutral. Methods: Investigators developed an item pool from previous measures. Items were screened by an expert panel for 'essentialness' to measuring HRQOL, and for functional bias. Remaining items underwent phases of: 1) cognitive testing; 2) bias testing using differential item functioning (DIF) analyses; and 3) field testing with a large national sample. Phase three data were subjected to factor analysis, IRT analysis, item-total correlations within domains (physical, mental, social, spiritual), and DIF analyses for gender, racial, and ethnic bias. Results were reviewed by an expert panel to select the best-performing items among those with similar content. The selected items were then administered twice to a sample of 100 individuals to assess test-retest reliability. Results: Analyses of phase three data indicated high internal consistency (>0.90) of domain scales, excellent fit to an IRT model, and few items showing bias. Elimination of problematic and redundant items resulted in a 41-item scale. Test-retest correlations were ≥ 0.85, indicating good short-term stability. Conclusions: The function-neutral health-related quality of life measure demonstrates strong psychometric properties and little bias. It can be used with the general population as well as groups with functional limitations.