No measure is perfect for the purpose of summing up the health of a
population; each way of estimating it violates one or another desirable criterion.
The two principal approaches are the burden of disease, which measures
losses of good health compared to a long life free of disability, and
some measure of life expectancy, adjusted to take account of time lived
with a disability. Both ways of summarizing health use the same information
about mortality and disability, and
both are related to a survivorship
curve, such as the bold line between
the areas labelled Disability and Mortality
in the figure.