Measuring the Sensitivity and Construct Validity of 6 Utility Instruments in 7 Disease Areas
Background. Health services that affect quality of life (QoL) are increasingly evaluated using cost utility analyses (CUA) These commonly employ one of a small number of multiattribute utility instruments (MAUI) to assess the effects of the health service on utility. However, the MAUI differ significantly, and the choice of instrument may alter the outcome of an evaluation. Aims. The present article has 2 objectives: 1) to compare the results of 3 measures of the sensitivity of 6 MAUI and the results of 6 tests of construct validity in 7 disease areas and 2) to rank the MAUI by each of the test results in each disease area and by an overall composite index constructed from the tests. Methods. Patients and the general public were administered a battery of instruments, which included the 6 MAUI, disease specific QoL instruments (DSI) and 6 other comparator instruments. In each disease area, instrument sensitivity was measured 3 ways: by the unadjusted mean difference in utility between public and patient groups, by the value of the effect size, and by the correlation between MAUI and DSI scores. Content and convergent validity were tested by comparison of MAUI utilities and scores from the 6 comparator instruments. These included 2 measures of health state preferences, measures of subjective well being and capabilities, and generic measures of physical and mental QoL derived from the SF 36. Results. The apparent sensitivity of instruments varied significantly with the measurement method and by disease area. Validation test results varied with the comparator instruments. Notwithstanding this variability, the 15D, AQoL 8D, and the SF 6D generally achieved better test results than the QWB and EQ 5D 5L.
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