Valuation of quality of life in rheumatoid arthritis

Abstract

The increased use of patient-reported outcome measures in health care, including measures of health-related quality of life (HRQoL), warrant the evaluation of the psychometric properties of these instruments. HRQoL instruments are frequently carried out within an economic analysis of health technologies. For this purpose, HRQoL instruments that measure valuations of health states (‘utilities’) from a societal perspective are preferred, such as the EuroQol-5D (EQ-5D) and the Short Form-6D (SF-6D). Although research has addressed the psychometric performance of these instruments, further research is required into the responsiveness of these instruments to improvements in patients’ health. In this thesis, both the responsiveness of the EQ-5D and that of the SF-6D in RA patients with active disease treated with effective TNF-blockers were only moderate over a one-year period. Less research has been carried out into the psychometric properties of instruments, such as Time Trade-Off (TTO) and Standard Gamble (SG), which measure utilities from a patient perspective. Existing research in RA shows poor psychometric properties. Because patients have a unique and full knowledge of, and experience with, their own health condition and are directly affected by interventions, we believe that it is important to obtain patients’ valuations. In this thesis, both the interview and computer TTO were poorly correlated with, and were poorly discriminative for, self-reported health outcome measures. The TTO asks patients about the number of life years they are willing to trade off, i.e. to die earlier, in return for perfect health. It is assumed that the more life years they are willing to trade off, the worse their health state is. An important explanation for the poor construct validity could be the fact that RA patients are less willing to trade any of their life years because they do not perceive their disease as life-threatening. Possibly, there are more realistic health-related anchors for RA patients. A qualitative and quantitative study of RA patients in this thesis showed that the scenario ‘being dependent on others’ was the most appropriate worst-case alternative. This thesis has given suggestions to improve the measurement of HRQoL representing the patient perspective and the societal perspective.