Public Health

Life expectancy is the average number of years that a person of a given age can be expected to live. It is typically measured hypothetically from birth, assuming that for individuals born in a specific year will have an age-specific death rate from the year of birth that will apply throughout the lifetime of a person born in that year.

How is Life Expectancy Calculated?

Life expectancy is calculated by constructing life tables. A life table incorporates data on age-specific death rates for the population in question, which requires enumeration data for the number of people, and the number of deaths at each age for that population. Those numbers typically are derived from national census and vital statistics data, and from them the average life expectancy for each of the age groups within the population can be calculated.

Period life expectancy (PLE) is a summary measure of current and overall population health. It is based on the set of observed age-specific death rates, i.e., the number of deaths in a certain year and age group divided by the average number of people alive in this year and age group. These death rates are then transformed into probabilities of dying and connected to a survival function from birth to the highest age in which people are living. The mean age at death is the period life expectancy (PLE). It can be interpreted as the average number of years that newborns of a certain period would live under the hypothetical scenario that the prevailing age-specific death rates remain constant in the future.

Cohort life expectancy (CLE) connects the age-specific death rates experienced by a cohort, longitudinally over its entire life course. CLE reflects the actual mean age at death of real people who were born at the same time. Therefore, CLE can only summarize past mortality experiences, whereas PLE reflects the most current death rates cross-sectionally across all ages.

What Impacts Life Expectancy?

Cohort life expectancy can be impacted by "cohort effects", or health conditions a specific cohort faces at a given time that can have an immediate or delayed impact on that specific cohort's mortality. These effects include exposure to disease, malnutrition due to wars and famine, radiation exposure due to nuclear accidents, and a variety of health behaviors such as diet, physical activity, alcohol consumption, and smoking. Since these effects are not consistent across the population and often can take years or decades to emerge, they can be difficult to account for when calculating life expectancy.

Period life expectancy can be impacted by a variety of period influences, most which can take years to impact mortality across a population, such as improvements in sanitation and hygiene, medical advances (vaccines, therapeutics), and increased access to healthcare.

Extreme external influences, such as wars, famines, natural disasters, and epidemics, can cause short term fluctuations to the overall life expectancy, through significant increases in mortality over a short period of time.

Life expectancy in most countries had sizable gains in the 20th century, however in most high-income countries the rate of life expectancy increases slowed at the beginning of the 21st century.

U.S. Life Expectancy decreased in 2021 for the second consecutive year, according to final mortality data released today. The drop was primarily due to increases in COVID-19 and drug overdose deaths.  The data are featured in two new reports from CDC’s National Center for Health Statistics (NCHS).

In the United States, life expectancy in 2020 plummeted a shocking 1.8 years, from 78.8 in 2019 to 77.0 in 2020. What was even more shocking was that while peer countries rebounded in 2021, life expectancy in the United States continued to decline to 76.4 years, the lowest life expectancy seen since 1996.

In 1980, life expectancy at birth in the U.S. and in comparably large and wealthy countries was similar, but over recent decades, life expectancy has improved by much more in peer nations than it has in the U.S.

Life expectancy around the world decreased in 2020 due to COVID-19. Most peer countries rebounded by 2021, while the U.S. continued to decline.While nearly every other industrialized country saw a life expectancy rebound during the second year of the COVID-19 pandemic after the arrival of vaccines, the United States did not.

Across the lifespan, and across every demographic group, Americans die at younger ages than their counterparts in other wealthy nations.

Shorter Lives, Poorer Health

In 2013 a research panel convened including the National Academy of Sciences and funded by the National Institutes of Health, to compare U.S. health and death with other countries, publishing a landmark 400-page report entitled "Shorter Lives, Poorer Health." The results glaringly showed that the U.S. was stalling on health advances in the population while other countries raced ahead.

The researchers were charged with documenting how Americans have more diseases and die younger and to explore the reasons why. The panel looked at American life and death in terms of the public health and medical care system, individual behaviors like diet and tobacco use, social factors like poverty and inequality, the physical environment, and public policies and values. "In every one of those five buckets, we found problems that distinguish the United States from other countries."

The researchers catalog what they call the "U.S. health disadvantage" – the fact that living in America is worse for your health and makes you more likely to die younger than if you lived in another rich country like the U.K., Switzerland or Japan.

A big part of the difference between life and death in the U.S. and its peer countries is people dying or being killed before age 50. The "Shorter Lives" report specifically points to factors like teen pregnancy, drug overdoses, HIV, fatal car crashes, injuries, and violence.

"Two years difference in life expectancy probably comes from the fact that firearms are so available in the United States," Crimmins says. "There's the opioid epidemic, which is clearly ours – that was our drug companies and other countries didn't have that because those drugs were more controlled. Some of the difference comes from the fact that we are more likely to drive more miles. We have more cars," and ultimately, more fatal crashes.