**3. Why measure health-related quality of life?**

Measuring HRQoL is becoming more widely accepted as a means of assessing the effects of chronic illness [18]. Physiological measurements are useful for physicians, but they are of little interest to patients, and they often have poor correlations with functional capability and well-being, which are the areas in which patients are most interested. Variations in exercise capacity among patients evaluated in the laboratory, for example, are very weakly connected to differences in the ability to conduct day-to-day activities in patients with chronic heart and lung illness [19]. Another reason to test HRQoL is the typical occurrence of two patients with the same clinical criteria having vastly different responses. Two patients with the same forced expiratory volume in 1 s and even the same exercise capacity in the lab, for example, may have different role functions and emotional well-being. While one patient may be able to continue working without experiencing sadness, another may be forced to leave their job and suffer from a major depression [19, 20].

These reasons explain why the impact of medical therapies on HRQoL are of great interest to patients, doctors, and healthcare executives [20]. HRQoL is of special importance to managers since the patient mix influences consumption and expenditure patterns. HRQoL is increasingly being used as a measure of care quality and clinical efficacy, and payers are beginning to factor HRQoL data into payment decisions.
