Content validity of preference-based measures for economic evaluation in chronic obstructive pulmonary disease

BACKGROUND: Generic preference-based measures (GPBMs) are health-related quality of life (HRQoL) measures commonly used to evaluate the cost-utility of interventions in healthcare. However, the degree to which the content of GPBMs reflect the HRQoL of individuals with chronic obstructive pulmonary disease (COPD) has not yet been assessed. The purpose of this study was to examine the content and convergent validity of GPBMs in people with COPD. METHODS: COPD patients were recruited from healthcare centers in Ontario, Canada. The Patient-Generated Index (PGI) (an individualized HRQoL measure) and the RAND-36 (to obtain SF-6D scores; a GPBM) were administered. Life areas nominated with the PGI were coded using the International Classification of Functioning Disability and Health and mapped onto GPBMs. RESULTS: We included 60 participants with a mean age of 70 and FEV1% predicted of 43. The mean PGI score was 34.55/100 and the top three overarching areas that emerged were: ‘mobility’ (25.93%), ‘recreation and leisure’ (25.19%) and ‘domestic life’ (19.26%). Mapping of the nominated areas revealed that the Quality of Well-Being scale covered the highest number of areas (84.62%), Health Utilities Indices covered the least (15.38% and 30.77%) and other GPBMs covered between 46 and 62%. A correlation of 0.32 was calculated between the SF-6D and the PGI. CONCLUSIONS: The majority of GPBMs covered approximately half of the areas reported as being important to individuals with COPD. When areas relevant to COPD are not captured, HRQoL scores generated by these measures may inaccurately reflect patients’ values and affect cost-effectiveness decisions.