What does "life expectancy" really mean?

Unlike other wealthy countries, the United States is seeing its life expectancy drop, according to a report recently published in the Journal of the American Medical Association (JAMA).

Using data from the Centers for Disease Control and Prevention (CDC), the report states the average life expectancy of a child born in 2017 dropped to 78.6 years, down from 78.9 years in 2014.

What is life expectancy?

Life expectancy is a projection estimating what the average age of death will be for people born today. It is based on data regarding the health of the nation as well as estimates of the impact of current trends decades in the future.

While life expectancy is a projection, the average age of death and death rates are not. The latest data for these two measures supports the conclusion that US health is decreasing.

Here’s an explanation of what each of these terms mean:

Average age of death: This is based on the ages of everyone who died in a given year. The US death rate ranged between 72.2 years in 2004 to 73.2 years in 2013. In 2017, the average age of death fell to 73.1 years.

Death rates: This is calculated based on the proportion of people who died in a given year. A version of the death rate is the age-adjusted death rate, which accounts for population variations in different geographic areas. In 2017, the age-adjusted death rate was 731.9 out of 100,000 people. That’s up 0.4% from the 728.8 deaths per 100,000 in 2016.

Life expectancy: This calculation uses age-specific death rates. Life expectancy estimates how long a person is expected to live based on current data. (It does not measure the average age at which a person dies in a given year.) While the 0.3-year change in life expectancy between 2014 and 2017 may seem small, that expected decrease of three to four months in a newborn’s lifespan reflects actual health issues affecting thousands of Americans.

Life expectancy at birth and the average age of death

The JAMA report points out that the recent decrease in life expectancy is connected to a rise in death rates due to specific causes, including “drug overdoses, suicides and organ system diseases” specifically among younger adults, regardless of the racial group. Increases in death rates among younger people can lead to a decrease in life expectancy.

CDC data shows how this has changed. Between 2014 and 2017, the crude death rate — without adjustments — for 25- to 34-year-olds increased 23% (from 108.4 deaths per 100,000 people to 132.8 deaths per 100,000 people) while the crude death rate for 35- to 44-year-olds rose 11% (175.2 in 2014 to 195.2 in 2017.) While those age groups account for just 5% of the nation’s 2.8 million deaths in 2017, those increases in death rates were enough to lower life expectancy.Opioid addiction, deaths, and treatment: The latest analysis of the data

With CDC WONDER data, any changes to the primary death rate can be investigated further down to the cause of death. For 25- to 44-year-olds, the overdose death rate increased from 25.1 deaths per 100,000 people in 2014 to 40.2 deaths per 100,000 people in 2017.

While life expectancy is a regularly cited measure of the health of a country or other geographic area, it’s important to understand that the measure is a future estimate based on what’s happening with the population today. Life expectancy figures are based on a series of other data points—specifically death rates—that could be investigated further based on age, geography, cause of death and a number of other variables. Looking at such data helps public health decision-makers understand what is behind increases and decreases in the calculation of life expectancy.

CDC WONDER: 2018 data is scheduled for release in January 2020.

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