Assessments of health-related quality of life and particularly utility values are important components of health economic analyses. Several instruments have been developed to measure utilities. However no consensus has emerged regarding the most appropriate instrument within a therapeutic area such as chronic pain. The study compared two instruments - EQ-5D and SF-6D - for their performance and validity in patients with chronic pain.
Pooled data from three randomised, controlled clinical trials with two active treatment groups were used. The included patients suffered from osteoarthritis knee pain or low back pain. Differences between the utility measures were compared in terms of mean values at baseline and endpoint, Bland-Altman analysis, correlation between the dimensions, construct validity, and responsiveness.
The analysis included 1977 patients, most with severe pain on the Numeric Rating Scale. The EQ-5D showed a greater mean change from baseline to endpoint compared with the SF-6D (0.43 to 0.58 versus 0.59 to 0.64). Bland-Altman analysis suggested the difference between two measures depended on the health status of a patient. Spearmans rank correlation showed moderate correlation between EQ-5D and SF-6D dimensions. Construct validity showed both instruments could differentiate between patient subgroups with different severities of adverse events and analgesic efficacies but larger differences were detected with the EQ-5D. Similarly, when anchoring the measures to a disease-specific questionnaire - Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) - both questionnaires could differentiate between WOMAC severity levels but the EQ-5D showed greater differences. Responsiveness was also higher with the EQ-5D and for the subgroups in which improvements in health status were expected or when WOMAC severity level was reduced the improvements with EQ-5D were higher than with SF-6D.
This analysis showed that the mean EQ-5D scores were lower than mean SF-6D scores in patients with chronic pain. EQ-5D seemed to have higher construct validity and responsiveness in these patients.