Abstract P323: Comparison and Validation of Quality of Life Instruments in Optimally-Treated Stable Coronary Patients

Abstract

Background: Measures of quality of life and health status have become important outcomes in clinical trials and in economic evaluations of medical interventions. Even if these measures were from validated instruments, it is necessary to check the instruments' reliability and validity with on-going trial subjects. Methods: We used three years of data from the COURAGE study, a randomized trial evaluating the outcomes of optimal medical therapy (OMT) with or without percutaneous coronary intervention (PCI) in a total of 2,287 patients with stable Coronary disease. We assessed angina-specific health status via SAQ, overall physical and mental function via RAND-36, and a single, preference-based index measure of health via standard gamble based utility. Results: Intra-class coefficients for SAQ were from 0.33 to 0.53, for RAND-36 were from 0.45 to 0.69 in each domain, but was only 0.27 for utility, suggesting that SAQ and RAND-36 were assessments with good consistency and reproducibility, but utility was not. SAQ and RAND-36 were shown to be instruments with trusted internal consistency reliability: Cronbach's alpha values from subscale scores for SAQ were from 0.6 to 0.9, and for RAND-36 were from 0.77 to 0.93; for SAQ as an instrument of angina status were from 0.74 to 0.80, for RAND-36 as an instrument of general health status were from 0.90 to 0.93 across time. The coefficients of variation were 0.38 to 0.60 for each domain of SAQ and 0.33 to 0.82 for each domain of RAND-36, but less than 0.24 for utility across time, indicating that SAQ and RAND-36 reflected the impact of treatment over time, while utility did not. The Canadian Cardiovascular Society Classification, a widely used system for grading angina severity of symptoms, was highly related to baseline scores in each domain of SAQ and RAND-36, but not to the baseline utility, indicating that utility was problematic in measuring the differences in angina severity. Conclusions: For stable coronary patients, SAQ was the most reliable instrument in COURAGE, although there is need to consider variation of scores in each domain; RAND-36 while also reliable, was not as good for angina as SAQ; utility from standard gamble program was not a good instrument due to the ceiling effect and we should be cautions about its use.