Utility weights for the vision-related assessment of quality of life (AQoL)-7D instrument

Purpose: To obtain utility weights consistent with the needs of economic evaluation for the Assessment of Quality of Life (AQoL)-7D, a generic instrument created to increase the sensitivity of the measurement of quality of life amongst people with impaired vision. Methods: Two extant instruments were combined, the Vision-related Quality of Life Index (VisQoL) and the AQoL-6D. Utilities were obtained from patients with visual impairment and from the general population using time trade-off (TTO) methodology. Dimensions were combined and an econometric adjustment used to eliminate the effects of instrument redundancy. Bias was tested by comparison of holistic TTO values with utility scores predicted from the AQoL-7D scoring formula. Results: The AQoL-7D instrument consists of 26 items and 7 dimensions each with good psychometric properties. Their combination into a single instrument resulted in significant redundancy which was successfully eliminated. Utility formulae for both the public and patients produced bias-free estimates of the utility of holistic health states describing visual impairment. Results imply differing valuations of health states by the public and by people with impaired vision. Conclusions: The AQoL-7D can detect changes in health states affecting people with impaired vision which are likely to be overlooked by other generic instruments due to content insensitivity. The utilities it produces are generated using a mainstream methodology, the TTO. Quality-adjusted life year values based on the AQoL-7D may therefore be used for economic evaluation of programs.