LONG BEACH, Calif--Of the different types of economic analyses used in cost studies of medical therapies, only the cost utility analysis takes into account quality of life as an outcome, Jane Weeks, MD, said at the 1995 Quality of Life Symposium, sponsored by St. Mary Medical Center. To understand how this type of analysis works, physicians must add two new measurement units to their vocabulary: "utilities" and "quality-adjusted life years (QALYs)," she said.
Rather than using dollars or years of life saved as a measurement unit, cost utility analyses use QALYs, determined by plotting quality of life versus length of survival, said Dr. Weeks, assistant professor of medicine, Harvard Medical School, Dana-Farber Cancer Institute.
To use quality of life to adjust survival (so that 1 year of life at a "quality" of X is as desirable to the patient as 6 months of life at a "quality" of 2X), it must be measured as a "utility," which Dr. Weeks defined as a quantitative measure of the strength of a person's preference for an outcome. By convention, "utilities" are measured on a scale of 0 to 1, in which 0 represents death and 1 represents perfect health, she said.
Three major approaches have been used to determine utility scores: a rating scale, such as a visual analogue scale (see " Cost Utility Study Shows Value of Aggressive Antiemetic Use"), completed by the patient in response to questions; the standard gamble, in which the utility of a health state is assessed by asking the patient how much he or she would be willing to risk to improve it; and the time tradeoff, which asks how much time one would give up to improve quality of life. The point of indifference occurs when shortened life expectancy with perfect quality of life is equal to longer life expectancy with lower quality of life.
Since all three of these methods have problems that make them difficult to do in a clinical trial situation, Dr. Weeks offered an alternative method of determining utilities--the "multiattribute utility approach," or health indices.
In this approach, a standard quality of life questionnaire is administered and a formula is then used to convert the answers into a utility score. The formula is determined by surveying a reference population using standard gamble or time tradeoff techniques.
Several formulas are now available for generating utilities, Dr. Weeks said. At Dana-Farber, she is involved in developing a cancer-specific multiattribute scale known as the "Q-tility Index," based on Spitzer's Quality of Life Index (QLI), a five-dimension scale specific for cancer. "For any possible combination of answers to the QLI, you can generate a utility using the Q-tility Index," she said.
