In the past two decades a number of investigators have attempted to combine measures of mortality and morbidity in order to address issues of whether Americans are living longer, healthy lives, as well as just longer lives. In general, a life-table approach is used to divide increases in years lived into healthy and unhealthy years. These measures have the same useful characteristics as life-table measures based only on mortality. They can be compared across time and place, and they summarize a large amount of age-specific data. Because indicators of disability are the most frequently collected measures in surveys, they have been used most frequently to examine change over.
