Predicting QALYs gained due to weight loss (ie changes) Obesity affects patients' health-related quality of life (QoL) and has been shown to be associated with deteriorations in functional status and well-being.28, 29, 30, 31, 32 Utility scores offer an alternative method of QoL assessment. Utility refers to the worth of a health state and is measured by evaluating preferences by an individual or society for the given state. Utility scores go from 0 (death) to 1.0 (perfect health). Changes in states can be expressed in incremental utility terms and converted to QALYS. These units weight an individual's duration in a health state by the average utility of that health state. Thus if a patient with a severe illness lived for 10 y with a utility score of 0.3, this would be equivalent to 10 × 0.3 or 3 QALYs.
The effect of changes in BMI on patient utility was examined by Hakim et al33 using patient reported QoL and BMI data from a clinical study.34 Using a conversion algorithm developed by Torrance,35 the authors converted the QoL scores into utility weights and established that a one unit decrease in BMI over a 1-y period was associated with a 0.017 gain in utility (utils).33
The time horizon for evaluating QALY gains was based on a 3-y post-treatment perspective (see Other key assumptions). The weighted average gain in QALYs for the average orlistat patient is calculated using estimates of QALYs gained for orlistat responders and orlistat nonresponders and known percentages of responders and nonresponders with orlistat. The incremental QALYs gained for orlistat plus a calorie-controlled diet compared with a calorie-controlled diet (placebo) is calculated by subtracting QALYs gained with placebo from QALYs gained with average orlistat patient.