Background: Preference-based instruments are a specific type of health-related quality-of-life scale designed to measure the relative value of health. Because of this property, they are the appropriate measures of quality of life for cost-effectiveness analysis. Although preference-based scales are widely used, their validity has rarely been tested in specific patient groups.
Objectives: To assess quality of life using preference-based scales in a group of patients with PD and to compare these scores with measures of clinical severity and traditional quality of life.
Methods: Each patient was rated using the Disability and Distress Index (DDI), the Euroqol System (EQ-5D), and the Health Utilities Index Mark II (HUI). Clinical severity was measured using the Unified PD Rating Scale (UPDRS) and PD Questionnaire-39 (PDQ-39) quality-of-life instrument. Results from preference-based instruments were compared with each other and with clinical measures of disease severity.
Results: One hundred subjects participated in the study, and 97 completed all preference-based instruments. Scores from all three instruments correlated well with the UPDRS and most domains of the PDQ-39. The mean scores for the DDI, HUI, and EQ-5D were 0.92 (range 0 to 1), 0.74 (range 0.19 to 1), and 0.58 (range -0.429 to 1). Differences between mean scores for the instruments were significant.
Conclusions: In the sample of patients with PD, the Disability and Distress Index, Euroqol System, and the Health Utilities Index Mark II correlate well with measures of disease severity and quality of life. However, they give strikingly different values. When applied in cost-effectiveness analysis, these discrepancies could result in substantially different cost-effectiveness ratios for PD-related interventions.