Health related utility measurement in rheumatology: an introduction.

Utility measures of health-related quality of life are preference values that patients attach to their overall health status. In clinical trials, utility measures summarize both positive and negative effects of an intervention into one single value between 0 (equal to death) and 1 (equal to perfect health). These measures allow for comparison of patient outcomes of different diseases and allow for comparison between various health care interventions. There are two different approaches to utility measurement. The first is to classify patients into categories based on their responses to a number of questions about their functional status, as for instance the Quality of Well-Being questionnaire. The second approach is to ask patients to assign a single rating to their overall health by means of rating scale, standard gamble, time trade-off, or willingness to pay. The Quality Adjusted Life Year (QALY) as outcome measure includes both effects in terms of quality and quantity of life. Utilities are used as weights to adjust life years for the quality of life in order to calculate QALYs. Both QALYs and utilities are useful in decision-making regarding appropriate procedures for groups of patients.