Table of Contents

Introduction

Fertility

Mortality

Migration

Population Size and Growth

Population Composition

Population Distribution

Population Growth Issues

Concern About Population

Conclusion

Suggested Resources

References

Related Publications

Population: A Lively Introduction

Mortality

• Life Expectancy
• Figure 3: Life Expectancy at Selected Ages for Males and Females: Japan, 1995
• Life Span
• Mortality in the United States
• Table 1: The 15 Major Causes of Death: United States, 1995
• Mortality Differentials
• Age
• Figure 4: U.S. Death Rates by Age for Males, 1900 and 1996
• Sex
• Socioeconomic Status
• Minority Disadvantage

Mortality, the counterpoint to fertility, is the second cause of population change. The death rate for a population is usually expressed as the number of deaths per 1,000 persons in a given year. In 1997, 2.3 million Americans died out of a population of 267.6 million, producing a U.S. crude death rate of 9 deaths per 1,000 persons.

An estimated 53 million people died that same year throughout the world. With a 1997 global population of 5.84 billion, these deaths also produced a death rate of 9 per 1,000. Worldwide, death rates in the late 1990s ranged from only about 2 in Kuwait, Qatar, and the United Arab Emirates, to 30 in Sierra Leone.

The death rate measures the proportion of a population that dies each year, but comparing death rates among populations does not show whether one population is healthier or lives longer than another. The death rate is strongly influenced by the age structure of the population. Death rates often are higher in developed countries such as Sweden than in developing countries such as Nicaragua, even though developed countries tend to have healthier environments and better medical services. A large proportion of the population of developed countries is in the older ages—the ages at which most deaths occur—while a relatively small proportion of the population of developing countries is in the older ages. Forty-four percent of the population of Nicaragua is under age 15, when fewer deaths occur, and only 3 percent is age 65 or older. In contrast, only 19 percent of Swedes are under age 15, and 17 percent are ages 65 or older.

Life Expectancy

To better gauge the life chances of individuals in a population and to better compare mortality conditions among countries, we must look at the average life expectancy. Both biological and social factors influence how long individuals live, and by extension, the average life expectancy within a population. In 1996, the average life expectancy at birth in the United States was 76 years. Japan had the world's highest life expectancy in the late 1990s—80 years. The lowest life expectancy estimates for the late 1990s were 34 years for Sierra Leone and 36 years for Malawi.

Life expectancy is a concept many people use but few understand. What does the 1996 U.S. life expectancy of 76 years really mean, and to whom does it apply? The term life expectancy usually is used as a short-hand way of expressing "life expectancy at birth." Can we conclude that a child born in the United States in 1996 can expect to live to age 76, on average? Not really. As an infant born that year proceeds through life, mortality conditions will change. Individual lives may be cut short by war or a devastating plague of some new disease, or may be extended through fantastic medical advances.

Life expectancy at birth in 1996 applies to no real group, not even to real people born in 1996. Like the TFR, life expectancy applies to a hypothetical group of people who pass through their imaginary lives subject to the death rates at each age in 1996. Age-specific death rates refer to the number of deaths of persons within a specific age group divided by the total number of people in that age group. This can also be expressed as the probability of dying at a given age. These probabilities are used to construct a life table, or actuarial table, which is used to calculate life expectancy at birth or at any other age.¹⁷ At age 80, for example, a Japanese woman has more than nine additional years of life remaining, on average (see Figure 3). Having survived the major causes of death at younger ages, she has already demonstrated that she will live longer than the average.

Life Span

How high can life expectancy get? The upper limit is governed by the maximum life span for the human species. Although the two terms are often confused, life expectancy reflects the real-life conditions in a population, while life span is a theoretical maximum number of years the most robust humans can live.¹⁸ Many individuals outlive the average life expectancy for their society (12 million Americans were over age 76 in 1996), but no one outlives the maximum human life span.

Experts disagree about the upper limit of the human life span and about whether it is possible to push it to higher levels through medical technology or bioengineering.¹⁹ To our knowledge, the longest anyone has ever lived is 122 years, five months. This was the authenticated age of Frenchwoman Jeanne Calment when she died in 1997. There have been reports of people living much longer, but these claims are unsubstantiated and are highly suspect. The very old often exaggerate their age, and the recording of birth dates and ages is haphazard in many countries. Birth records were especially poor when the current centenarians were born.

The number and percentage of elderly who survive to extremely old ages is increasing and eventually someone is likely to break Madame Calment's record. In 1998, the reputed oldest living person was 118 years of age.²⁰

But relatively few humans are favored with a genetic makeup that will allow them to live past 100. Only one in every 100 Americans born in 1980 can expect to live past age 100.²¹ The average life expectancy for a national population has never exceeded 80, although continued declines in mortality among the elderly are likely to push that higher. Some demographers predict that the average life expectancy for a national population may never exceed 85 years, although unforeseen medical breakthroughs could raise that limit.²²

Many world regions still have extremely high mortality from easily curable diseases, but in nearly all countries people live much longer now than in the past. The average life expectancy in the world at the turn of this century was less than 30 years of age; in the late 1990s, it was 66 years. Thus, since the origin of modern humans some 100,000 years ago, the vast majority of progress in conquering mortality has taken place in the minute slice of time since 1900. Much of the increased life expectancy worldwide reflects the accumulation of knowledge about how diseases spread as well as improvements in personal hygiene and public health practices.²³

A large share of the remaining gap in mortality between developed and developing countries can be attributed to preventable diseases that strike children particularly hard, including diarrhea, respiratory infections, measles, and neonatal tetanus.²⁴ Antibiotics, immunization, and clean drinking water have drastically reduced the incidence and severity of these diseases in the United States and many other countries. If adequate health services were available throughout the developing world, mortality could fall quite rapidly.

National mortality levels can increase when health systems break down or when diseases spread to new populations. Life expectancy in Russia declined by more than six years after the breakup of the Soviet Union left public health systems in chaos and many Russians in poverty. Average life expectancy in Russia started a slow recovery in 1995.²⁵

HIV, the virus that causes AIDS, is spreading rapidly in sub-Saharan Africa and has already infected more than 21 million Africans. HIV/AIDS will cause life expectancy at birth to fall in several sub-Saharan African countries before the epidemic runs its course, reversing the gains in infant and childhood health achieved before the epidemic arose.²⁶

The HIV/AIDS epidemic is a grim reminder that the battle against communicable diseases will probably never be over. Many aspects of modern life—international air travel, importation of fruits and vegetables, migration, and even changes in climates—favor the spread of communicable diseases.²⁷

Natural disasters and widespread violence can also produce a spike in the number of deaths, but they usually have little long-term impact on mortality rates at the national level. Earthquakes, wars, fires, terrorism, hurricanes, and other disasters claim the most lives in less developed areas, where many people live in low-quality housing and where the public health and safety systems are limited.

Mortality in the United States

Life expectancy in the United States was age 76 in 1996, a spectacular improvement over an average life expectancy of only age 47 in 1900, but still nine years short of the theoretical maximum of 85 years.

How can mortality be reduced further in the United States? We need first to look at the causes of death. Table 1 lists the 15 leading causes of death in the United States that account for 86 percent of all deaths. Heart disease and cancer are the two biggest killers. Indeed, these two diseases are in a league by themselves; they are responsible for more than one-half of all deaths. Heart disease, cancer, and most of the other major causes of death strike primarily after age 50 rather than during childhood. But no one is immortal. All the progress in life expectancy has, after all, only postponed death.

Mortality Differentials

The Grim Reaper does not bring death to all on an equal basis. Death rates vary by common social categories such as age, sex, socioeconomic status, race, ethnicity, and religion. Cultural, political, and other social factors help explain the gap in life expectancy among different groups of people.²⁸ Genetic factors also explain why individuals with similar background characteristics die of very different causes and at different ages. Individuals can inherit a predisposition for developing a potentially lethal disease such as breast cancer. But demographic factors—especially age, sex, and ethnicity—are most closely tied to mortality rates.

Age

The death rate is relatively high during an infant's vulnerable first year of life, then it declines throughout childhood and early adolescence before starting an inexorable climb to a towering peak after age 85. From the point of view of the mythical Grim Reaper, Americans are most elusive at ages 10 and 11 when only one out of every 5,000 people dies, and most vulnerable at age 122 when virtually everyone is harvested.

Death in the first year of life (infant mortality) is an important demographic variable and is often used as a key measure of a society's quality of life. The infant mortality rate (IMR)—the number of deaths among infants under age 1 per 1,000 live births—has declined tremendously in the United States during the 20th century. In 1900, about 120 newborns died out of every 1,000 babies born alive. By 1997, the infant mortality rate was 7, low by world standards but still higher than in many European countries.²⁹ In countries where health care systems are inadequate and infectious diseases are rampant, the IMR often exceeds 100 deaths per 1,000 live births.

Once children survive that crucial first year and the next few years of childhood, their life chances improve substantially. Young Americans have barely a 1 percent chance of dying between ages 15 and 24. But in the 1990s, that 1 percent attrition means that 37,000 15-year-olds will never reach their 25th birthdays.

Most of these deaths are socially preventable. Indeed, the rank order of causes of death for 15-to-24-year-olds is very different from that shown in Table 1 for the entire population. Injuries cause the most deaths in this age group, led by injuries from motor vehicle crashes. Accidents,³⁰ homicide, and suicide are ranked one, two, and three, respectively, and accounted for a disturbing 76 percent of all deaths in that age group in 1995. Over the last three decades, death rates have declined for Americans, but not for the 15-to-24-year-olds. Why? A dramatic rise in violent deaths among young adults has offset reductions in other causes of death.

Sex

The sex differential in mortality rates is greatest for young adults. The death rate for 15-to-24-year-old males is nearly three times greater than that of their female counterparts. Notice first that all the leading causes of death listed in Table 1 kill males at a higher rate than females. Which causes have the highest male-to-female ratio? They are HIV/AIDS, which until recently mainly struck young men; suicide, which claims more than four times as many male as female lives; homicide, a killer especially of young black men; and accidents, or unintentional injuries, which tend to befall more young men because of their penchant for risk-taking behavior. In short, the sex differential in mortality is greatest between ages 15 and 24 because the major causes of death in those ages are also the ones with the highest male-to-female ratio.

Socioeconomic Status

Minority Disadvantage

African Americans die at younger ages than whites because they are more vulnerable to 11 of the 15 leading causes of death shown in Table 1. Note especially the ratio of black to white homicide death rates — the rate is six times higher for blacks than for whites.

Homicide is the chief cause of death for young black men, while young white men are most likely to die from injuries sustained in automobile crashes or other types of accidents.

Native Americans live about four years fewer than whites, on average. But minorities do not always have higher mortality. Hispanics have mortality rates close to U.S. national averages; and U.S.-born Asian Americans have a substantially longer life expectancy than white Americans. The life expectancy of recent Asian immigrants approaches that of the general population.