Vila et al. provides a comprehensive summary of the various methods that can be used to quantify death rates, including the crude death rate, age-specific death rates, age-adjusted death rates, years of potential life lost (YPLL), life expectancy, and others. Because there is no one best measure that captures all aspects of mortality, a judgment must be made based on which dimension of mortality is most useful for a particular application. Strategies such as age-adjustment may also be employed to facilitate comparisons across populations with different characteristics.
In contrast to more traditional death rates, YPLL emphasizes the processes underlying premature mortality in a population. The concept behind YPLL involves using the number of years of life (life-years) lost due to premature death, defined by a standard cut-off age in a population, to obtain a total sum of the life-years lost before ages 65, 75, or 85 (for example) for a population. There is debate over how “premature” death is defined and which age – 65, 75, or 85 – is most appropriate to use as the upper age limit for calculating YPLL.
Finally, while most mortality measures are ways of counting deaths, life expectancy can be thought of as an inverse measure of death, or a measure of how long a population is surviving on average. Since life expectancy changes with age and with time, life expectancy calculations are more complex than those required for calculating YPLL.
What Is the County Health Rankings Measurement Strategy?
The County Health Rankings program reports years of potential life lost (YPLL) as its measure of premature death, based on all deaths occurring before the age of 75. Each of these deaths contributes to the total number of years of potential life lost. For example, a person dying at age 50 would contribute 25 years of life lost to the YPLL index. Dranger and Remington provide a more detailed description of the YPLL calculation methodology. The YPLL is age-adjusted to the 2000 U.S. population to allow comparison between counties and is reported as a rate per 100,000 people. Three-year averages are used to create more robust estimates of mortality. YPLL rates are calculated from data in the National Vital Statistics System and are provided by the CDC’s National Center for Health Statistics.