the U.S. population, the committee adopted quality-adjustment weights representing the HUI Mark II-based age- and sex-specific health status results from the Canadian NPHS (Wolfson, 1996). These weights reflect population-based values calculated from self-reported features of health status. They range from .93 for men aged 15–24 to .64 for women aged 85 and older. The separate NPHS health status estimates for men and women were combined as a weighted average based on the age-specific proportions of men and women in the U.S. population. Since NPHS did not produce health status estimates for the population younger than 15 years of age, the committee chose, in the absence of other data, to apply the value for ages 15–24 to the younger age groups. See Table 5–1 for the quality adjustment weights for health status of the general population.
Life Expectancies The discounted quality-adjusted life expectancies used in the committee’s analysis are based on the 1993 abridged U.S. life tables for the total population and for males and females separately (National Center for Health Statistics, 1993). These adjustments were incorporated through calculations that use the life table stationary population in each age interval (the nLx values, in life table notation), which can also be interpreted as the number of person-years lived from ages x to x+n. The quality adjustment was incorporated by multiplying the number of person-years by the corresponding age- and sex-specific quality-adjustment weight for the population (Sullivan, 1971; Erickson et al., 1995):
nLx*=wx• nLx. (5)
The quality-adjusted person-years in each age interval were then discounted for the period between age at the onset of a condition and the midpoint of the age interval. Because the average age at onset for the conditions under study varies from infancy to older than 70 years, a series of life expectancy calculations were made for selected ages at onset (0, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, and 85 years of age). The discounting period was defined as the difference between the midpoint of the age interval and the age at onset. For example, the discounting period for person-years lived in the age interval 60–65 with disease onset at age 20 was 42.5 years (62.5–20=42.5).
Once the discounted person-year values were obtained, standard life table calculations were used to calculate discounted quality-adjusted life expectancies at the selected ages of onset,* with life expectancy at age x designated as ex*.
To calculate life expectancies, the person-years lived are summed from the oldest to the youngest ages. For each age interval, a cumulative total of all person-years lived in that interval and at all older ages is obtained. Dividing the cumulative total for age interval x (designated Tx) by the number of persons in the life table population alive at the beginning of that age interval (lx) gives the life expectancy (ex) at age x. See Erickson et al. (1995) for additional discussion and illustration of life table calculations incorporating quality adjustments.