Health-adjusted life expectancy

Health-adjusted life expectancy for a population can be calculated by combining estimates of the average health of an individual in each of its age groups with the life table for that population (Salomon, Wang, Freeman et al. 2012).

The average health of each age group age, H_x, is assigned a value between 0 and 1 calculated from the estimates of the prevalence in that age group of the 220 health states considered by the GBD study and the disability weights assigned to them:

$$H_x=1-\sum _{h=1}^{220}{W}_h·p_{h,x}$$

This measure of healthy life differs from that used in the calculations of healthy life expectancy that were described in sessions PAPP101-S08 and PAPP104-S03. In the current calculation, H_x takes a value between 0 and 1 which reflects the full range of disabling conditions affecting the population, each of which can differ in its severity.

The earlier method considered only a single form of ill-health. For example, the population might be divided into the sighted and the blind or into those with no or only slight disability and those with moderate or severe disability. Each living individual was categorised either as healthy (e.g. sighted), and assigned a weight of 1, or as unhealthy (e.g. blind), and assigned a weight of 0. Thus, the average state of health of age group x was simply the proportion of the age group that was not disabled:

$$H_x=1-p_{h,x}$$

where h refers to the form of disability being studied. Thus, the earlier measure of healthy life expectancy is perhaps best conceptualised as a measure of the expectation of life free of a specified disability.

The health-adjusted life tables are calculated using Sullivan’s method (see session PAPP101_S08 ). Health-adjusted life expectancy (HALE) at birth is calculated by multiplying the person years lived in each age group, x, in the life table for the population, L_x, by the health value of that age group and summing these health-adjusted life years across all ages:

$$HAL{E}_0=\frac{\sum _0^{\infty }{H}_x·L_x}{l_0}$$

This measure was termed disability-adjusted life expectancy (DALE) by the first burden of disease studies.

While DALYs are an absolute measure of health that reflect the size and structure of a population, the HALE of a population is not affected by its age structure. Thus, the HALE is a suitable summary measure with which to compare the overall level of health in different populations.

Subtracting health-adjusted life expectancy from overall life expectancy provides an age-standardised estimate of the healthy years lost to disability by the population.