Mortality (demography)

Mortality is the branch of demography that studies rates and causes of deaths for a population as a whole.

Measuring mortality

Death happens to everyone, but sooner is worse than later. The various measures of mortality are used to compare conditions between localities and between groups of people. Groups or localities with high mortality rates call out for special attention. A decline in the rates is a gauge of progress. All the mortality rates are based on simple division—the number of people who die divided by the number at risk of dying in that group or locality.

Life Span

Lifespan refers to the highest possible old age (120 or more) and is of relevance mostly to those interested in curiosities such as those reported The Guinness Book of Records. Of more interest to students of population is longevity, or, the ability to stay alive. Medicine is focused on increasing longevity which is measured for a population by life expectancy. Although the formulas for calculating life expectancy are rather complicated (because they depend on an accurate life table), in a nutshell the concept is simple. The life expectancy of a group at birth is a hypothetical number. It represents the average age of death of the group, assuming that today’s death rates will stay the same with no improvements. Worldwide, the life expectancy for a new baby is 65 years. That is, life expectancy calculations assume people in the future course of their lifetime will encounter the today’s mortality rates for children, teenagers, and adults.

See life expectancy

In reality, death rates usually fall. The life expectancy was 77.2 years for babies born in the US in 2001. But back in 1970 the life expectancy at birth was 71 years. People born in 1970 will actually live longer than 71 years, but how much longer depends on how far the age-specific death rates fall in the future; in 2041 the babies of 1970 will be 71 years old and who knows what medicine will be like then? Life expectancy researchers fall into three camps: those who see life expectancies reaching 85 years, then level off; those who argue that mortality will decline at about 2 percent per year to create life expectancies of 95 to 100 by the year 2080; and finally those visionaries who predict that new biomedical breakthroughs will increase life expectancies to 150 to 200 years. No one forsees a situation like Russia in the 1990s, where life expectancy has been falling.

Crude Death Rate: CDR

Crude Death Rate (CDR) refers to the total number of deaths in a given year divided by the average (or midyear) total population, times 1000. The CDR does not take age into account, so a healthy country with many old people may have a higher CDR rate than an unhealthy country with a young population. The CDR for the United States steadily declined from 17.2 deaths per 1000 in 1900 to 9.6 deaths per thousand population in 1950, then stayed frozen for 20 years. (Even though people were healthier, the population was getting older.) Since 1990 the CDR has been steady at about 8.5 deaths per 1000 per year.

Age-specific death rate (ASDR)

Age-specific death rate (ASDR) refers to the number of deaths each year for a specific age group, divided by the average number of people in that year of that age or the midyear total population. If two populations have different age distributions, the ASDR is better than the CDR to evaluate mortality. The calculation of the ASDR requires age data from the census in addition to vital statistics data. Assembling all the ASDR's together for every year of life produces a life table.

Death rates in graph of a life table are U-shaped or J-shaped, When infant mortality is high, it is U-shaped. As infant mortality declines, the left side of the U falls and the curve looks more like a J-shape. Death rates are always lower in the middle years (age 10-45), then rise rapidly in a developing country, or rise slowly in a rich country.

Overall, the main reason for the rise in world population is the decline in the death rate (not rising fertility). This decline is called the "epidemiological transition" and is one of the great success stories of modern medicine and public health. The epidemiological transition occurs when the pattern of deaths in a country switches from communicable/infectious diseases to degenerative diseases and accidents.

Determinants of Mortality

Deaths are caused by infectious diseases, by degenerative diseases or by violence (such as suicide, accidents and homicide.) The causes vary greatly across countries and across the centuries.

The World Health Organization promulgates the International Classification of Diseases, (ICD) which every country uses. Therefore it is possible to compare mortality in different countries. Before the ICD became standard, death certificates varied widely even when describing the same symptoms. However, death statistics are well kept only in the richer nations, and before 1900 were rarely well kept anywhere. Note that the classification focuses on the disease that was the immediate cause of death (such as lung cancer) and not on whatever caused the disease (such as smoking).

Infectious Diseases

Infectious diseases are caused when an outside organism invades the body. Diseases caused by germs--that is, bacteria or protozoa. Although there are plenty of disease germs in the air, water and soil around us, disease can be prevented by sanitation and vaccines, and cured with antibiotics. Programs to vaccinate everyone against smallpox and measles, and to immunize against diphtheria, tetanus, German measles, and polio have been highly effective. (Smallpox is gone and polio will disappear very soon—once all the germs are dead the disease is finished forever.) Unfortunately, there are no cures for diseases caused by viruses, such as the common cold or AIDS.

HIV/AIDS

AIDS is a new disease that, like tuberculosis in the 19th century and cancer in the 20th century, became the focus of dread because of its devastating effects. The disease originated in monkeys but jumped to humans in Africa in the 1950s. It spread slowly until the early 1980s, when it suddenly exploded as one of the deadliest and most horrible diseases in history. In 2006, worldwide 40 million people were infected with HIV and 2.9 million died. More than 25 million people have died of AIDS since 1981, with the heaviest burden in Africa, where there are 12 million AIDS orphans. The mortality is 100%, though in recent years drug therapies have been developed that slow its progress. AIDS is caused by the human immunodeficiency virus (HIV) virus. The virus spreads primarily via sexual intercourse (mostly heterosexual intercourse with prostitutes in Africa and Asia, and homosexual intercourse in the North America and Europe), and through the sharing of needles used to inject heroin. About 20-30% of children of infected mothers catch the disease. A peculiar characteristic of this disease is that the HIV virus usually lies dormant for five or ten years, then explodes into the AIDS disease, which attacks the T4 white blood cells and thereby destroys the body's immune system in one to three years' time. The public health problem is that people unaware they carry the HIV virus may spread the disease for years, thereby creating an epidemic. The number of cases in the United States peaked at one-half of one percent of the population. The annual number of deaths peaked in the U.S. in 1995 at 42,500 and declined steadily to 14,000 in 2002. In 2003 the U.S. launched a 5-year program, spending $15 billion for prevention, treatment and care of AIDS patients in developing countries.

AIDS deaths are increasing in Africa and Asia. An estimated 34-47 million people carried the HIV virus in 2006, 60% of them in Africa, and 20% in South Asia. In Africa six countries have adult infection rates over 20%. Estimates from 2003 show South Africa has 5,300,000 cases; India has 5,100,000; and Nigeria has 3,600,000. The U.S. has 950,000 cases.

Tuberculosis

Tuberculosis (or "TB," "consumption," "scrofula," "white death") was in the industrial era a terrible scourge, reaching epidemic proportions. It is an infectious disease, spread by coughing; crowded living conditions facilitate its spread. Cattle can carry the disease and infected milk is a public health threat, solved by government inspection of cattle and mandatory pasteurization of milk. TB strikes people in their 20s and 30s. A century ago. as “consumption” it had a highly romantic connotation in novels and opera--the death of the young lover. Since 1900, however, as “TB” it has been identified realistically with filth and squalor. Long term rest in special hospitals was the only cure before the arrival of highly effective antibiotics in the 1940s. TB cases have dropped steadily in the US, reaching a low of 15,100 new cases in 2002, over a third of them from immigrants. There were over 100,000 cases annually in the 1940s. The number of deaths fell to 800 in 2002, compared to 70,000 a year in the 1930s, and 150,000 a year in 1900-1910. In 1900 TB was the second leading cause of death, right behind pneumonia. Upwards of 10 or 15 million people in the United States today have latent TB; those most at risk of contracting the disease itself are HIV (AIDS) sufferers. In developing countries tuberculosis remains a major cause of death, especially in crowded slums.

Degenerative Diseases

Everyone dies of something sooner or later, and the decline in young deaths from infectious diseases means an increase in deaths from degenerative disease at a later age. Degeneration means the body's wear and tear over the decades leads to greater risks. Of course, it is possible to prolong life and lower the death rate for everyone.

Heart disease

By far the leading killer in the United States, accounting for 918,000 deaths in 2002 (37% of all deaths), is heart disease. The major cause is hardening of the arteries, or atherosclerosis (pronounced ath-uh-roh-skluh-ROH-sis). Layers of plaque build up on the inside of coronary arteries. The plaque is comprised of cholesterol, lipids, and cellular debris. Too much plaque will reduce the flow of blood to the heart muscle, which eventually gives out in a heart attack (myocardial infarction).

Atherosclerosis is a normal part of aging, and begins about ten years earlier in men than women, and this is the major reason women live longer. The rate of plaque buildup varies greatly, even among people with similar diets; a family history of heart attacks is a bad sign. The onset may appear to be sudden, because a blockage of the arteries are wider than they have to be, and a narrowing of the arteries of more than 75% is needed to impede blood flow seriously. If enough plaque has built up, there is grave risk that a clot will come along, block all blood, and kill the affected organ—which might be the heart or the brain. High blood pressure (hypertension) and high blood-cholesterol are warning signs. Obesity and cigarette smoking weaken the body’s natural resistance; diabetes raises the level of blood lipids and speeds the buildup of plaque.

To avoid or postpone atherosclerosis physicians recommend the elimination of cigarette smoking, a reduction of dietary saturated fat, a reduction in high blood pressure, more exercise, and weight control. Perhaps Americans are heeding this advice; the age-adjusted annual death rate from heart disease plunged from 559 deaths (per 100,000) in 1960 to 240 in 2002, and it continues to fall. In addition to life style changes, major credit goes to advances in surgery, especially balloon angioplasty (which widens the artery by flattening the plaque) and bypass surgery (which routes blood around the blockage). Survival of patients who reach the hospital has improved markedly, but about one-third of the 1,500,000 Americans who have a heart attack each year will die. About 250,000 people will die from their heart attack before they reach the hospital. For people who survive a heart attack, about 20% of women and 16% of men will have another during the next four years.

Similar to heart disease, but counted separately, is stroke or cerebrovascular accident (CVA). It is the third most common cause of death, taking 163,000 American lives in 2002. It involves a sudden impairment of brain function, usually caused by atherosclerosis or a blood clot that cuts of the flow of blood to the brain. Stroke affects the brain, while a heart attack affects the heart. About half the fatal strokes come before age 70. Smoking, high cholesterol, diabetes, aging, and heritable defects make stroke more likely. The death rate fell in half between 1970 and the 1990s, perhaps due to better diets, exercise, and less smoking. If not immediately fatal a stroke may be more or less debilitating; therapy is often successful.

Cancer

Cancer (malignant neoplasms) is the second most common cause of death in the United States, with 559,000 deaths in 2002. Although known to antiquity, cancer was not a major killer until the 20th century, when it replaced tuberculosis as the most dreaded disease. The incidence varies dramatically across the world. The main causes of cancer are environmental hazards such as radiation exposure, pollutants and chemicals, especially asbestos and nicotine. There are about 150 varieties of cancer, affecting different organs. A few rare forms of cancer are caused by viruses, but in general it is not an infectious or communicable disease. Over a million new cases a year are diagnosed, and about half these people survive five years. The most common types are lung cancer (with only 12% surviving 5 years), breast cancer (80% survival), colon cancer (60%), and prostrate cancer (80%).

Violence

Violence as a cause of death includes accidents (especially traffic accidents), suicides (especially of older men), and homicide (especially of younger men.) Violence is the leading cause of death in the US between ages 1 and 45, when cancer takes over. Violent deaths have been declining in developed countries in recent years, but have been rising in developing countries, especially as automobiles become widespread.

Social factors

Social factors have to be considered when dealing with mortality. The society's promotion of tobacco usage will have a major impact on the death rate from lung cancer, emphysema, and heart disease. In 2002 25% of American men and 20% of American women smoked, and nearly one-fifth of deaths from cardiovascular illnesses are attributable to smoking. Smoking doubles the risk of having a heart attack. Society’s tolerance for alcoholism will show up in accident rates and diseases such as cirrhosis of the liver. Happily, smoking and alcoholism have been declining in recent decades.

Diets are a factor. The Mediterranean diet with a low consumption of saturated fat, meat and milk, but a high consumption of fruit, vegetables and carbohydrates, is considered healthy. This diet probably explains why Albania, although a very poor country, has a high adult life expectancy. Diets have improved, from a medical standpoint, in the last 30 years for all groups and classes in the United States. This is especially true for high income people who used to eat too much fatty steak, and have now switched to more chicken and fish. The cardiovascular death rates for U.S. men and women are about double those reported from Japan and France, which is probably due to diets.

Deaths Worldwide

Worldwide, there are about 50 million deaths a year (with 6 billion people, this gives a CDR of 8.4 deaths per 1000). Life expectancy is about 65. Ninety-eight percent of all deaths of children occur in the developing world, along with 83% of deaths at ages 15-59, and only 59% of deaths over age 70. The probability of death between birth and 15 years ranges from 22% in sub-Saharan Africa to 1% in the developed economies. Probabilities of death between ages 15 and 60 range from 7% for women in developed countries to 39% for men in sub-Saharan Africa. Worldwide in 1990, infectious disease accounted for 17.2 million deaths, degenerative diseases for 28.1 million deaths; and violence for 5.1 million deaths. The leading causes of death were heart disease (6.3 million deaths worldwide), strokes, (4.4 million deaths), lower respiratory infections (4.3 million), diarrhoeal diseases (2.9 million), perinatal disorders (2.4 million), chronic obstructive pulmonary disease ("COPD", includes emphysema and chronic bronchitis) (2.2 million), tuberculosis (2.0 million), measles (1.1 million), road-traffic accidents (1.0 million), and lung cancer (0.9 million).

The decline in mortality in developing countries is due primarily to public health measures and the availability of cheap but powerful antibiotics and other drugs. How the decline takes place is best explained by the “Epidemiological Transition.”

The Epidemiological transition

The Epidemiological transition or Mortality Transition comes when the pattern of deaths in a country switches from communicable to degenerative and accidental. Evidence from skeletons suggests that premodern mortality in hunting and gathering cultures was very high, with bad nutrition a major factor. (People who are starving are highly prone to many diseases; they do not usually die of starvation itself.) Many hunting tribes simply died out all together.

The agricultural revolution produced a much larger and more certain food supply; it also produced more face-to-face interactions, which allowed infectious diseases to spread rapidly.

The pneumatic plague or "Black Death" that hit Medieval Europe in the 14th century was caused by a bacillus and was spread by coughing; nearly all the victims died in a few days time. When the plague hit in 1348, Europe’s population had been growing steadily for over 300 years. The plague killed 75 million, or about a third of the overall population, and in some districts it killed 70-80% of the people. Europe’s economy and society was radically altered; suddenly there was surplus of land and a shortage of farm laborers. Not until 1500 did Europe again reach the population it had in 1348.

Bubonic plague is a slightly milder variety, involving the same bacteria, but is spread by fleas and rats; before the 20th century 60-90% of the victims died in a matter of days. Plague still occurs in isolated areas, but is cured by immediate application of antibiotics, and seems to be much less lethal than in the past.

Colombian Exchange

Colombian Exchange. The almost total isolation of the Western and Eastern hemispheres meant that when Christopher Columbus initiated travel back and forth, new and devastating germs traveled along. Far more Europeans traveled the ships, so the disease flow was primarily from east to west. The native populations of the Western Hemisphere were especially vulnerable to the new diseases of smallpox and measles. The Indians had not built up immunity over the centuries, and so the death toll was horrific. In the territory that became the United States, the population of many tribes fell 75 to 90%, and many tribes vanished all together.

Industrial Revolution to present

The sanitary conditions in practically all cities in the 19th century were breathtakingly bad. Thousands of newcomers crowded together, sharing the same water, sanitation and germs, leading to very high rates of communicable diseases. Infant mortality was 150-200 per thousand births. The rapidly growing industrial cities had very few old people. Thomas McKeown, a British historical demographer, has downplayed the role of medicine and health professionals in the epidemiological transition. Instead, he argues, rising incomes meant better nutrition and better personal hygiene. Crop failure no longer meant famine because cities could buy and ship food from far away. There have been no famines in Western Europe since the Irish "potato famine" of the 1840s. Other historians, however, point out that the just one disease, smallpox, accounted for 10 to 20% of all deaths in rural England in 1750, and for very few in 1800. The reason was the successful effort by physicians to promote mass inoculation in the villages of England (and in other parts of Europe as well). Inoculation meant injecting a mild form of smallpox to enable a person to build resistance; it certainly was an effective preventative. An alternative interpretation to McKeown, presented by Preston and Haines emphasizes the role of health personnel, especially physicians, nurses and public health workers. They used the new communications media and new prestige accorded science and experts to preach the advantages of personal and community hygiene.

Physicians had very few effective drugs before the 1940s. Versatile sulfa drugs arrived in the 1930s to combat infectious diseases caused by bacteria. Even more powerful drugs, antibiotics arrived in the 1940s--penicillin, streptomycin, amoxicillin, tetracycline, and many others. They were effective treatments for diseases caused by bacteria, and immediately had a major impact on infectious diseases. Highly effective, quick streptomycin therapy replaced long-term bed-rest as a cure for tuberculosis in the 1940s. Death rates plunged from tuberculosis and pneumonia. Operations became much safer thanks to antibiotics and the use of blood transfusions. Developing countries

The decline in mortality in developing countries is due primarily to public health measures and the availability of cheap but powerful antibiotics and other drugs. Accidents, especially involving automobiles, are fast becoming a major cause of death in the developing countries. Alcohol, poor highways, and bad driving behavior have been implicated.

For as far back as there are records, famines were common every few decades in societies that had not industrialized. Famines killed millions in the Ukraine in the early 1930s, and in Bengal (part of India) in 1943-44. In 1959-61, widespread crop failure in China caused 14 to 30 million deaths. Severe famines have hit parts of Africa repeatedly in recent decades. In the late 1990s North Korea was suffering severe malnutrition if not famine. In the Malthusian model, famine is caused by the interaction of overpopulation and fluctuating food supplies. However, in most cases, political factors such as warfare or civil war were deeply implicated in causing and prolonging the distress.

Table 1 Crude Death Rates by Cause

to come

Age patterns

Infant mortality

see Infant mortality

Infant mortality rate (IMR) refers to the number of deaths in the first year of life per 1000 live births. In 2007 the rates ranged from a low of 2.3 in Singapore, to 4.8 in the European Union and 6.4 in the U.S., to a high of 184 in Angola. The world average was 43.5 deaths per 1000 births.

The decline in infant mortality is one of the most impressive events of the 20th century. In 1900, one-fourth of American babies died before they reached age 5; today 99% survive to age 20. Today most of the deaths are perinatal (within one week of birth), and are caused by congenital abnormalities (birth defects), sudden infant death syndrome, respiratory distress syndrome and complications from very low birth weight. Historically infants and children under 6 were especially at risk for respiratory and gastrointestinal infections, which did not yield to medicine until antibiotics arrived.

The poorest countries of the world have the highest IMR, especially sub-Saharan Africa. In Somalia and Afghanistan civil wars have caused famines and disrupted public health and medical services. Respiratory distress, diarrhea, malaria and malnutrition are the main causes of infant mortality in this region.

In the developed world, Japan, Sweden and Singapore have the lowest IMR. The astonishing recent advances in caring for premature babies means that a child born under two pounds in a rich country has an excellent chance of survival. The infant deaths that still occur in rich countries happen chiefly in the first month after birth (neonatal mortality). The main causes of infant mortality in these countries are congenital deformity, sudden infant death syndrome, respiratory distress syndrome, and effects of very low birth weights.

Death at older ages

Young adults, are most likely to die by violence, especially automobile accidents, homicide and suicide. In the 1980s AIDS became a major factor for young adults. For every cause of death the mortality for males was much higher than for females (except cancer, where the risks were about equal).

By age 50, cancer is the leading causes of death for men and women, equalled for men by heart disease. By age 70-74, heart disease and cancer remain by far the major killers, with the addition of stroke and chronic lung disease (from smoking).

Social status differentials

Race

The crude death rate for whites is slightly higher than the rate for African Americans. But that is because whites are older: the median age of whites in 1995 was 35.3 years, compared with 29.2 years for blacks. Age-adjusted black mortality rates are 60 percent higher than white rates. Of ten leading causes of death, the rates are higher for whites only for suicide and chronic obstructive pulmonary diseases (emphysema and bronchitis). The rate of death from strokes and diabetes is twice as high for blacks as it is for whites. The rate for conditions originating during the perinatal period is three times higher. For AIDS the African American rate is four times higher. Furthermore, blacks are almost seven times more likely than whites to be murdered.

In 1994, only 4 percent of U.S. deaths were to persons of Hispanic origin, although Hispanics made up more than 10 percent of the entire population. Because of heavy immigration of young adults from Mexico and other Latin countries since 1980, Hispanics are the youngest minority group. Their median age in 1995 was just 26.2 years.

Social Status

The more money, information, education, access and prestige a person has, the better health for the family. Additional years of schooling reduce mortality. Apart in violent episodes, very few people die at work (only 50 deaths per million per year). Therefore the main occupational difference is exposure to serious accidents (or, in the case of taxi drivers and convenience store clerks, to homicide.) The risk of fatal accidents is highest for fishermen, lumberjacks and pilots of small planes. Among economically developed nations, there is no correlation between average income and life expectancy. Inside each country, however, the better educated, higher income groups live longer. For example, for men age 35-64, the poorest have a death rate about 11% higher than the richest (in large part because people in poor health earn much less money.) Overall, high income white men live about two years longer than low income white men.

Gender Female life expectancy is higher, and the differential has been growing. (In the US, from a gap of 2 years in 1900 to one of 7 years in 2001.) The reasons are unclear, but doubtless involve biological advantages (females develop heart disease 10 years later than men) and social ones (females are less exposed to dangerous jobs, and historically drink less liquor and smoke less tobacco.) In large parts of Korea, India and China, boy preference leads to discrimination against girls, and female babies are much more likely to die.

Urban and Rural Differentials

Before 1900 or so, conditions in cities were unsanitary; death rates were higher than in rural areas because infectious diseases could spread faster and to more victims. In the 20th century public health programs in the cities of the developed world have been highly successful in reducing infectious diseases. The programs have focused on pure water, pasteurized milk, sewer systems, personal hygiene, quarantine of sick patients, more hospitals, home nursing, and education of the public about hygiene and health matters.

Counterfactual history

Demographers Kevin White and Samuel Preston have estimated what the American population would have been if improvements in health care and life expectation had suddenly stopped. That is, they froze the death rates at 1900 levels and projected the population in 1920, 1940, 1960, 1980 and 2000. (They also froze the levels of 1920, 1940, 1960 and 1980 to see what would happen.)

In 1900 the United States population was 81 million, and life expectancy at birth was 47 years. Column A of the table can be read as follows: Assume there was no improvement after 1900. That is, death rates are frozen at 1900 levels. Column B assumes that death rates froze at 1920 levels, column C at 1940 levels, column D at 1960 levels and column E at 1980 levels. The population in 1920 was actually 114 million, but it would have been only 109 million. In 1940 the actual population was 139 million, but it would have been 134. In 1980 the actual population was 230 million, but it would have been only 137 million. In 2000 the actual population will be about 276, but it would be only 139 million. In other words if death rates froze at 1900 levels, there would only be half as many Americans alive today.

Table 2: White-Preston Estimates US Population, Millions 1900-2000

Table 2 to be inserted here

Source: Kevin White and Samuel Preston, "How Many Americans Are Alive Because of Twentieth-century Improvements in Mortality?" Population and Development Review (1996) 22:415-429

Table 3: Epidemiological Transition and Major causes of death

Table 3 to be inserted here

Bibliography

• CIA World Factbook, 2007. online
• Fogel, Robert W. The Escape from Hunger and Premature Death, 1700-2100: Europe, America, and the Third World (2004)
• Omran A.R. "The epidemiologic transition: a theory of the epidemiology of population change." Milbank Memorial Fund Quarterly (1971) 49:501-538
• Arthur Haupt and Thomas T. Kane. Population Handbook (Population Reference Bureau, 5th ed. 2004) online (5th ed. 2004), A quick 72pp guide to population dynamics; explains how to calculate and use major rates, ratios, and other measures from the birth rate to the life table; includes tips on interpreting population data.
• Riley, James C. Rising Life Expectancy: A Global History (2001)
• Shryock, H.S. and Jacob S. Siegal. The methods and materials of Demography. (1978) Chapter 14 and 15.
• Weeks, John R. Population: An Introduction to Concepts and Issues (10th ed. 2007)
• Wendel, Helmut, and Christopher S Wendel. Vital Statistics of the United States Births, Life Expectancy, Deaths and Selected Health Data (2006)
• Yaukey, David and Douglas L. Anderton. Demography: The Study of Human Population. 2nd ed. 2001. Chapter 5

External resources

• Richard Jensen, World Population: A Guide to the WWW
• Population Reference Bureau

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