Patient utilities in chronic musculoskeletal pain: how useful is the standard gamble method?

The main goal of current pain management approaches is to increase the pati ents' quality of life by improving pain coping skills and by reducing the l evels of disability in daily life, often despite persistent pain. Direct me asurement of quality of life is of crucial importance in economic evaluatio n research, in which not only is the estimation of financial costs and bene fits included, but so is the evaluation of costs and benefits in terms of c hanges in health states. The purpose of this study is to compare the psycho metric qualities of two instruments for assessing patients' utilities, the rating scale (RS) and the standard gamble (SG). Such instruments are design ed for their application in economic evaluation research, but have seldomly been used in chronic pain trials. Both methods provide a single measure be tween 0 and 1. The relationship between these utility measures and descript ive and domain-specific quality of life measures was examined in 133 fibrom yalgia patients and 148 patients with chronic non-specific low back pain, M ean utility score at baseline was 0.43 with the RS and 0.78 for the SG, The correlation between both methods was found to be poor (r = 0.21). Both mea sures appeared to be fairly stable in a 2-week test-retest period (intra cl ass correlation coefficient (ICC) = 0.74 and 0.77). Scores on the descripti on of patient's own health on six domains, global assessment of change and domain specific measures correlated moderately with the RS scores and low w ith the SG. Multiple regression analyses demonstrated that 32% of the varia nce in RS values and only 13% of the variance in SG utilities could be expl ained by domain-specific measures. These results suggest an acceptable cons truct validity for the RS but insufficient construct validity for the SG, V aluations of ones own health appear only partially to be related to the ass essment of the pain-specific measures and measures of distress. it can be c oncluded that the RS and domain-specific measures assess partly different, but nevertheless complementary aspects of health-related quality of life. I t is therefore recommended to include in economic evaluation studies both d omain-specific measures and valuation measures. Finally, in chronic musculo skeletal pain patients, RS scores were found to be more responsive in detec ting significant changes in preferences than SG scores. For use in patients with chronic musculoskeletal pain, the RS is preferred to the SG for estab lishing accurate decisions about the impact of new interventions on their h ealth outcomes. (C) 1999 International Association for the Study of Pain. P ublished by Elsevier Science B.V.