The assessment of health-related quality of life has developed significantly since the 1970's. Among the instruments that assess overall HRQOL, only a few can be used for cost-utility analysis. Cost-utility analysis is defined as cost-effectiveness analysis (CEA) that uses QALYs as the outcome. QALYs have been identified as the preferred outcome metric by Gold et al. (1996) in hopes of standardizing CEAs in medicine and healthcare. As mentioned above, QALYs incorporate both quality of life and mortality into one score which allows for comparisons across diseases and populations. In the past, CEAs have used a variety of outcomes, thus often making comparisons difficult. Standardization of outcomes, definitions, and methods of CEA is an important step for integrating findings.
The Quality of Well-being (QWB) scale was the first instrument specifically designed to measure quality of life for the estimation of QALYs. The QWB is a preference-weighted measure combining three scales of functioning with a measure of symptoms and problems to produce a point-in-time expression of well-being that runs from 0 (for death) to 1.0 (for asymptomatic full function). Most HRQoL measures focus on functioning; the QWB and QWBSA have a functioning component complemented by a strong symptom component. Prior work by our group demonstrated that on any particular day, nearly 80% of the general population is optimally functional. However, fewer than half of the population experience no symptoms. Symptoms or problems may be severe, such as serious joint pain, or minor such as taking medication or following a prescribed diet for health reasons.
The QWB was developed using theory from the General Health Policy Model (Kaplan, 1993b, 1993c; Kaplan & Anderson, 1996; Kaplan, Anderson & Ganiats, 1993). This model includes several components, including mortality (death) and morbidity (health-related quality of life). In several papers, Kaplan and colleagues have suggested that diseases and disabilities are important for two reasons: first, illness may cause life expectancy to be shortened, and second, illness may make life less desirable at times prior to death. Thus in assessing the impact of a health intervention, one must measure both a possible decrease in mortality as well as an improvement in health. In addition to mortality and morbidity, the General Health Policy Model incorporates preference for observed health states (utility) and duration of stay in health states (prognosis).
Utility studies looking at how people value health have been conducted to place the observable states of health and functioning onto a preference continuum for the desirability of various conditions, giving a "quality" rating between 0 for death and 1.0 for completely well. A Quality-Adjusted Life Year (QALY) is defined as the equivalent of a completely well year of life, or a year of life free of any symptoms, problems, or health-related disabilities. Consider, for example, a person who has a set of symptoms and is in a state of functioning that is rated by community peers as 0.5 on a 0.0 to 1.0 scale. If the person remains in that state for one year, he or she would have lost the equivalent of 1/2 of one year of life. Thus, a person limited in activities who requires a cane or walker to get around the community would be hypothetically rated at 0.50. If he or she remained in that state for an entire year, the individual would lose the equivalent of one-half year of life. However, a person who has the flu may also be rated as 0.50. In this case, the illness might only last three days and the total loss in QALYs might be 3/365 X 0.50 which is equal to 0.004 QALYs. This may not appear as significant an outcome as the more disabled person. But suppose that 5,000 people in a community get the flu. The well years lost would then be 5,000 x .004 which is equal to 20 years of perfect health in one person. The quality-adjusted life expectancy is the current life expectancy adjusted for diminished quality of life associated with dysfunctional states and the duration of stay in each state.
By administering the QWB before and after a treatment or intervention program, the intervention can be described in terms of the quality adjusted life years that it produces or saves. When costs are examined (using standardized methods), every intervention can be given a cost/QALY value. This value delineates how much it costs, on average, to produce an extra QALY for each subject in a given study.
Several studies have demonstrated that the QWB is responsive to clinical change in a variety of patient populations. For example, QWB scores have been shown to be associated with health improvements in patients with cystic fibrosis (Orenstein, et al., 1989), chronic sinusitis (Hodgkin, 1994), and cochlear implant (Harris, et al., 1995). In addition, the QWB is responsive to medications expected to have a minor effect, such as oral gold treatment for patients with arthritis (Bombardier, et al., 1986) or medications that have a larger effect, such as AZT for patients with HIV infection (Kaplan, Anderson, Wu, et al., 1989). Other applications of the QWB include chronic obstructive pulmonary disease (Kaplan, et al., 1984), AIDS (Kaplan, et al., 1989), diabetes mellitus (Kaplan, et al., 1987), atrial fibrillation (Ganiats, et al., 1992), lung transplantation (Squier, et al., 1994), cancer (Kaplan, 1993a), depression (Kaplan, 1997), schizophrenia (Patterson, et al., 1996), fibromyalgia (Kaplan, Schmidt, and Cronan, 2000), osteoarthritis (Groessl, Kaplan, and Cronan, 2000), and several other conditions (Kaplan, 1993b). Further, the method has been used for health resource allocation modeling and served as the basis for the innovative experiment on rationing of health care by the state of Oregon (Kaplan 1993b, 1993c).
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