Life expectancy is a common and important population health outcome measure and can be easier to interpret than other mortality measures.
Life Expectancy is an Average
Life Expectancy measures the average number of years from birth a person can expect to live, according to the current mortality experience (age-specific death rates) of the population. Life Expectancy takes into account the number of deaths in a given time period and the average number of people at risk of dying during that period, allowing us to compare data across counties with different population sizes.
Life Expectancy is Age-Adjusted
Age is a non-modifiable risk factor, and as age increases, poor health outcomes are more likely. Life Expectancy is age-adjusted in order to fairly compare counties with differing age structures.
What Deaths Count Toward Life Expectancy?
Deaths are counted in the county where the individual lived. So, even if an individual dies in a car crash on the other side of the state, that death is attributed to his/her home county.
Some Data are Suppressed
A missing value is reported for counties with fewer than 5,000 population-years-at-risk in the time frame.
Life Expectancy includes mortality of all age groups in a population instead of focusing just on premature deaths and thus can be dominated by deaths of the elderly. This could draw attention to areas with higher mortality rates among the oldest segment of the population, where there may be little that can be done to change chronic health problems that have developed over many years. However, this captures the burden of chronic disease in a population better than premature death measures.
Furthermore, the calculation of life expectancy is complex and not easy to communicate. Methodologically, it can produce misleading results caused by hidden differences in age structure, is sensitive to infant and child mortality, and tends to be overestimated in small populations.[3,4]
This measure can be used to measure progress with some caveats. Life Expectancy is a very long-term health outcome, effects on which might not be seen for years or even decades. Life Expectancy as a measure also changes much more minutely than other mortality measures due to its calculation. Coupling these matters with the 3-year average provided in the County Health Rankings means that small changes, especially in small communities, may be difficult to detect.
Years of Data Used
National Center for Health Statistics - Mortality Files
Data on deaths and births were provided by NCHS and drawn from the National Vital Statistics System (NVSS). These data are submitted to the NVSS by the vital registration systems operated in the jurisdictions legally responsible for registering vital events (i.e., births, deaths, marriages, divorces, and fetal deaths). In prior years of the Rankings, Premature Death was calculated by the National Center for Health Statistics, but this year the Mortality-All County (micro-data) file was requested. This allowed us to calculate Premature Death and Life Expectancy ourselves. While most calculations of mortality rates can be downloaded from CDC WONDER, the calculation of Years of Potential Life Lost and Life Expectancy requires raw data files.
 Centers for Disease Control and Prevention. Premature mortality in the United States: Public health issues in the use of years of potential life lost. MMWR Morb Mortal Wkly Rep. 1986;35(suppl 2):1S-11S.
 Dranger E, Remington P. YPLL: A Summary Measure of Premature Mortality Used in Measuring the Health of Communities. Madison, WI: University of Wisconsin Population Health Institute; 2004. Issue Brief 5(7).
 Silcocks PB, Jenner DA, Reza R. Life expectancy as a summary of mortality in a population: statistical considerations and suitability for use by health authorities. Journal of Epidemiology & Community Health. 2001 Jan 1;55(1):38-43.
 Eayres D, Williams ES. Evaluation of methodologies for small area life expectancy estimation. J Epidemiol Community Health 2004;58(3):243–9.