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.
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.
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.
The COVID-19 pandemic triggered an unprecedented rise in mortality that translated into global life expectancy losses in 2020 of a magnitude not observed in recent history in high-income countries. Data from low and middle income countries is more limited, but as evidence emerges, it suggests even greater losses than those of high-income countries. Only very few countries did not witness declines in LE in 2020, including Norway, Denmark, Finland (for females only), New Zealand and Australia.
While estimates from much of western Europe suggest that there will be at least partial recovery from the losses observed in 2020, other countries, including the U.S. will likely experience further life expectancy declines.
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.
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).
“Mortality in the United States: 2021” features the first public release of final mortality data for 2021, and the report documents that there were 3,464,231 total deaths in the United States during 2021 — 80,502 more than the total reported in 2020.
The death rate for the entire U.S. population increased by 5.3% from 835.4 deaths per 100,000 population in 2020 to 879.7 in 2021. As a result, life expectancy at birth for the U.S. population decreased from 77 years in 2020 to 76.4 years in 2021.
The 10 leading causes of death in 2021 were largely unchanged from 2020, except chronic liver disease and cirrhosis became the 9th leading cause of death in 2021 while influenza and pneumonia dropped from the list of 10 leading causes. Heart disease remained the leading cause of death in the United States, followed by cancer and COVID-19.
Estimates of excess deaths can provide information about the burden of mortality potentially related to the COVID-19 pandemic, including deaths that are directly or indirectly attributed to COVID-19. Excess deaths are typically defined as the difference between the observed numbers of deaths in specific time periods and expected numbers of deaths in the same time periods.
The National Center for Health Statistics (NCHS) Provisional Death Counts for Coronavirus Disease (COVID-19) visualizations provide weekly estimates of excess deaths by the jurisdiction in which the death occurred. Weekly counts of deaths are compared with historical trends to determine whether the number of deaths is significantly higher than expected.
Counts of deaths from all causes of death, including COVID-19, are presented. As some deaths due to COVID-19 may be assigned to other causes of deaths (for example, if COVID-19 was not diagnosed or not mentioned on the death certificate), tracking all-cause mortality can provide information about whether an excess number of deaths is observed, even when COVID-19 mortality may be undercounted. Additionally, deaths from all causes excluding COVID-19 were also estimated.
Note: Data for recent weeks is incomplete. Only 60% of death records are submitted to NCHS within 10 days of the date of death, and completeness varies by jurisdiction.
In many parts of the world, official death tolls under-count the total number of fatalities. As COVID-19 has spread around the world, people have become grimly familiar with the death tolls that their governments publish each day. Unfortunately, the total number of fatalities caused by the pandemic may be even higher, for several reasons.
One way to account for these methodological problems is to use a simpler measure, known as “excess deaths”: take the number of people who die from any cause in a given region and period, and then compare it with a historical baseline from recent years. We have used statistical models to create our baselines, by predicting the number of deaths each region would normally have recorded in 2020 and 2021.