Mortality

Types of death rate

Cause of death

World mortality—situation and trends

Death rates by age

Expectation of life

Death rates by marital status

Death rates by sex

Death rates by cause of death

BIBLIOGRAPHY

Mortality statistics are by-products of the legal process of death registration [seeVitalStatistics]. These data serve various purposes, such as estimating a component of population growth and preparing population projections; delineating health problems, planning public health programs, and assessing health progress; and studying the natural history of disease.

The absolute numbers of deaths are useful as a direct measure of the attrition of the population due to deaths. However, for analytical purposes, death data are generally used in the form of ratios. Properly computed, a death rate expresses the force of mortality on the population at risk.

Types of death rate

The crudest form of death rate is the total or general death rate. This is the number of deaths occurring in a particular period of time, usually a year, for each 1,000 persons in the area or population. Because the general death rate (often called the crude death rate) is the mean of the death rates by age, sex, color, and other demographic variables weighted by the demographic composition of the population, an area with a young population, for example, would have a low general death rate, and an area with an old population a high general death rate, even if the set of age-specific death rates for the two areas were the same.

In order to take into account the differential mortality by age, sex, or other demographic variable, death rates are usually computed for a specific population class or group. The age-specific death rate is an example of this type of rate. In some cases, comparisons are based on death rates adjusted for differences in population composition. If the rate is standardized for differences in the age composition of two populations, it is called an age-adjusted death rate.

A special kind of death rate is the life table death rate. This is a hypothetical set of derived death rates based on certain assumptions of mortality in a stationary living population unaffected by migration or births. One function of the life table which is of interest is the expectation of life. This is the average number of years that will be subsequently lived by a group of persons who have attained a certain age. The expectation of life at birth is the average age at death of all the 100,000 who start life together in the life table cohort. Another important function is the survival rate, which is the probability that persons of a particular age will survive for a particular period of time, usually a calendar year [seeLifetables].

Cause of death

An important aspect of mortality statistics relates to data derived from the medical information reported on death certificates. Despite their limitations, statistics on causes of death have contributed a great deal in the past to the field of public health [seePublichealth].

The present statistics on causes of death relate to the “underlying cause of death,” which is the term used to denote the disease or injury that initiated the train of events leading directly to death; in the case of accident or violence, it may also include the circumstances which produced the fatal injury. These statistics have done good service for public health in the past; but, with the lessening importance, at least in the United States, of the acute infectious diseases as compared with the chronic noninfectious diseases, the data have become less and less adequate. The selection of a single disease entity as the “underlying cause” poses a real problem in deaths involving chronic diseases, since in such cases it is frequently difficult, if not impossible, to identify a single underlying cause.

International comparison of cause-of-death statistics also presents a problem. In addition to differences arising from incompleteness of death registration in various countries, there are variations in proportion of deaths attended by a physician, in diagnostic acumen of the clinician in attendance, and in the recording of diagnostic information. International comparisons are further complicated by differences in medical concepts of diseases and in the methods of classifying causes of death. In fact, strict international comparability of cause-of-death statistics is at present a virtual impossibility, and too much significance should not be attached to small differences in rates between countries.

World mortality—situation and trends

The estimated annual death rate for the world population is 17 per 1,000 population for the period 1958–1962. As might be expected, the death rate varies over a wide range in different parts of the world (see Table 1).

If differences in the age composition of the population in various parts of the world were taken into account, the mortality differential would undoubtedly be much greater than that indicated by the crude death rates shown here. Unfortunately, the

data needed to compute age-adjusted death rates are not available for the various regions of the world. In fact, one of the serious problems in international mortality studies is the lack of adequate mortality statistics for a large part of the world. By and large, reliable data are available only for the countries of northern and western Europe, North America, and Oceania. With a few notable exceptions, data for countries in other regions are either very incomplete or nonexistent.

The estimated birth rate for the world population is a little more than twice the estimated death rate. The natural rate of population increase (the difference between the birth and death rates) is highest in the Latin American countries, followed by the countries on the African continent and in Asia. Traditionally, a major part of annual population growth comes from the contribution made by births, but one of the significant demographic developments in the recent postwar period is the sharp acceleration in population growth due to the rapid decline in mortality. Virtually all countries, and more particularly the developing countries, experienced unprecedented declines in mortality while their birth rates remained at a high level.

The rate of decline in world mortality following World War n was dramatic, but the death rate began to level off in the 1950s in a number of countries, such as the United States, England and Wales, Sweden, Norway, Finland, the Netherlands, Japan, and Chile. Intensive studies of the mortality trend for the United States (U.S. Dept. of Health, Education, and Welfare ... 1964a), Chile (U.S. Dept. of Health, Education, and Welfare ... 1964b), and England and Wales (U.S. Dept. of Health, Education, and Welfare ... 1965) indicate that a large part of the acceleration in the decline of general mortality was due to the large reduction in the death rate for infective and parasitic diseases as a result of antimicrobial therapy. In the United States, for example, the death rate for infective and parasitic diseases reached a low level, and by the mid-1950s it was no longer significantly influencing the general mortality trend. At the same time, the mortality trend for chronic diseases and for violence was either rising, remaining unchanged, or declining very slowly. This combination of circumstances causes a marked deceleration in the downward trend of the general death rate.

Whether this change in the mortality pattern is transient or permanent is difficult to say. It is obviously not possible for the death rate to decline indefinitely. Further reductions in mortality appear possible in the United States, but it does not seem likely that large declines will occur until a major breakthrough is made in the prevention of deaths from chronic diseases. On the other hand, if the age-specific death rates in the United States were to decline to levels already achieved by several other countries of low mortality, the crude death rate for the United States in 1960 would have been 7.3 per 1,000 population, as compared with the recorded death rate of 9.5 per 1,000 population. For males the expected death rate would have been 7.8, as compared with the recorded rate of 11.0 per 1,000 population. For females the corresponding rates would have been 6.9, as compared with 8.1 per 1,000 population.

The leveling off of the death rate as it reaches its irreducible minimum is readily understandable. However, there seems to be no ready explanation for the change in mortality trends at different levels. For example, the death rate for nonwhites in the United States is still considerably higher than that for whites. Yet the rate of decline of the mortality trend for nonwhites has slowed down in the same manner as that for the whites.

National death rates are also becoming stabilized at different levels. For example, the Scandinavian countries and the Netherlands have achieved much lower age-specific death rates than the United States, whereas the age-specific death rates for Japan and Chile are higher. Yet the death rates appear to be leveling off in all of these countries.

The experience of Chile appears to have important implications for the developing countries. It seems clear that the knowledge and technical means are available for securing significant reductions in the death rate even in developing countries. The institution of mosquito and fly control and/or the widespread introduction of antibiotics for therapeutic purposes will have an immediate impact upon the death rate. However, it would appear that a point of diminishing returns will soon be reached and the decline in mortality come to a halt. Accordingly, the study of mortality trends in Chile points to the importance of planning health activities as a part of the social and economic development of the country (U.S. Dept. of Health, Education, and Welfare ... 1964b).

Death rates by age

Reference was made earlier to the unsatisfactory nature of the crude death rate, which is significantly affected by the age composition of the population to which it refers. Death rates computed for various age groups, as in Table 2, are, of course, free of this problem.

As indicated by these age-specific death rates, infancy is the most critical period of life, even for

a developed country like the United States. Although data are not available to demonstrate this point, it would not be surprising if one-quarter or more of all live births in many of the developing countries fail to survive the first year of life.

For the developed countries it is possible to assess the progress made in the reduction of the infant mortality rate. A significant decline in infant mortality has occurred, and remarkably low rates have been achieved by the Netherlands (15.3 per 1,000 live births in 1962), Sweden (15.8 per 1,000 live births in 1961), and Norway (17.9 per 1,000 live births in 1961). A recent study (Shapiro & Moriyama 1963) of the international infant mortality trends indicates that the rate of decline is slowing up in many countries of low mortality.

From a relatively high death rate at infancy, the risk of death drops to a minimum at age ten or so. From then on, there is an increase in mortality with increasing age. This is the typical crosssectional pattern of mortality in countries of low mortality. However, there are a number of countries where the infant mortality rates are lower than that for the United States. Except in extreme old age, lower death rates are also found at other ages in other countries of low mortality.

In countries of low mortality, most of the deaths occur in the older age groups. In the developing countries, by contrast, it would not be unusual for more than half of all deaths to occur among children under five years of age. Under these conditions, it is obvious that the expectation of life at birth could not be very great.

Expectation of life

The Biblical life span of “three-score years and ten” has become the norm for a number of countries. In Sweden, Norway, Denmark, the Netherlands, and Israel the life expectancy at birth is 70 years or more for both males and females. In other countries, such as the United States, Canada, Czechoslovakia, France, England and Wales, Australia, and New Zealand, the average length of life of 70 years or more for the total population has been attained only because of the favorable mortality experience of females. For example, the average expectation of life at birth in the United States for 1962 is 73.4 years for females and 66.8 years for males. If up-to-date life tables were available for all countries, it is probable that a few other countries could be added to the list above.

The world situation with regard to longevity cannot be described with any precision. However, it seems clear that longevity is at present greatest in the northern and western European countries, Canada and the United States on the North American continent, and Oceania. The average life expectancy is less favorable in the central, eastern, and southern European countries. Still lowei on the scale are the Latin American countries. The average expectation of life for a large part of the Asian population is low, although an average length of life of 60 years or more may be found in such Asian countries as Japan, Nationalist China (Taiwan), and Ceylon. Life table values for many of the countries on the African continent are not available. The question in a good part of Africa, especially in the southern and tropical countries, is not longevity but survival through childhood.

The increase in longevity of the population in the developed countries has been considerable. For example, in the period 1900–1902 the average expectation of life at birth in the United States was 48 years for males and 51 years for females. In a period of some sixty years, the male population gained about 19 years in life expectancy at birth, while the gain for females was about 22 years.

The postwar increase in life expectancy has been spectacular for some countries. For example, the expectancy of life at birth in Ceylon increased from 46.8 years in 1945–1947 for males to 60.3 years in 1954. For females, the corresponding figures were 44.7 years and 59.4 years, respectively. The average annual gain in longevity in Ceylon, as compared with the experience in the United States, is therefore roughly five times greater.

Death rates by marital status

Almost without exception, the mortality among the married 20 years and over is lower, age for age, than the corresponding death rates for the single, widowed, or divorced. This is true for both males and females. Beyond this, the pattern of

mortality differentials by marital status varies somewhat by country.

In countries like Sweden, the mortality among divorced males is higher by far than the corresponding rates for bachelors or widowers (see Table 3). For females, the differences in death rates between the single, widowed, and divorced are not so great as those observed for males. The higher mortality among the single has been explained on the basis of selection; that is, those who never marry because of some serious physical impairment or chronic disease have a higher risk of mortality than the married. The single may therefore include among their number a higher proportion of the poorer mortality risks than those who marry. The higher mortality among the widowed has been attributed to the high association of diseases from which both marital partners die or to a less favorable economic situation that they both share.

One of the problems in the interpretation of death rates by marital status is the fact that the informant may not always know the civil status of those living alone. Also, there is the problem of the lack of correspondence between the marital status reported on death certificates and on the census enumeration schedules. Because the married population constitutes a large part of the total population, errors in reporting of marital status affect the data for the married much less than the data for the single, widowed, and divorced.

Death rates by sex

One of the significant constants of mortality statistics in countries of low mortality is the favorable experience among females as compared with that of males. Examination of death rates by sex for a recent year indicates large sex differentials in mortality for the United States and Canada (36 and 38 per cent, respectively) and for New Zealand and Australia (23 and 26 per cent, respectively). In the countries of western Europe the male mortality exceeded the death rate for females by 10 to 20 percent.

The death rate for females is lower than that for males in each age group from birth to the end of the life span in virtually every country of low mortality. Even in the developing countries the mortality experience among females is generally favorable as compared with males, except in the child-bearing ages. Maternal mortality is a significant public health problem in these countries, as it was in the developed countries some forty or fifty years ago.

It is not clear why female mortality is consistently lower than that among males. One obvious explanation is the biological difference between the sexes; however, biological differences do not appear to account for much of the sex differential in mortality. A good part of the difference in the death rate appears to be due to the increasing mortality among males or to the fact that the death rate among females is declining faster than that among males. Whatever the explanation for this phenomenon, the continued occurrence of the large sex difference in mortality as recorded in a number of countries will have important consequences in terms of the sex composition of the population of the future, especially in the older ages.

Death rates by cause of death

At the turn of the century, infective and parasitic diseases constituted the major public health problems in the world population. Pneumonia and influenza, tuberculosis, diarrhea and enteritis, and the childhood diseases were the principal causes of death in 1900, even in economically developed countries.

The large reduction in mortality since 1900 has been achieved primarily through control of the infective diseases. Although influenza and pneumonia still remain significant public health problems, mortality from the chronic diseases has

come to the forefront. The results of the review of causes of death in selected countries of North America, Europe, and Oceania in 1961 are summarized in Table 4.

From Table 4 it may be seen that more than 60 per cent of all deaths in the developed countries are attributable to the cardiovascular diseases and to malignant neoplasms. Although accidents rank fourth, they constitute the leading cause of death in the age groups 1 to 44 years; malignant neoplasms are the most frequent cause of death in the age group 45 to 64 years; and heart disease the principal cause of death in the population 65 years and over. Similar data for selected countries of Africa, South and Central America, and Asia for 1960 are shown in Table 5.

The number of countries in Africa, Asia, and South and Central America that met the criteria for inclusion in the World Health Organization compilations is limited, and the 12 countries that were selected do not, by any means, represent the mortality problems in the vast population of these continents. Although gastritis, duodenitis, enteritis,

and colitis were the leading causes of death for half of the selected countries, their average death rate and the proportionate mortality are relatively low. A principal cause of death that accounts for only about 9 per cent of all deaths and five leading causes that constitute no more than one-third of all deaths do not suggest any major health problems. Actually, the averages conceal some of the problems indicated by the data for individual countries. For example, the death rate for gastritis, duodenitis, enteritis, and colitis was 700 per 100,000 population in the United Arab Republic, and 36 per cent of all deaths were charged to these intestinal infections.

Adequate mortality statistics for these regions would delineate existing public health problems more clearly. If such statistics were available, it is likely that other infective diseases, such as tuberculosis, dysentery, typhoid, and measles; parasitic diseases, such as schistosomiasis and malaria; and possibly malnutrition and other dietary deficiency diseases would figure prominently as causes of death.

With the availability of knowledge and means for controlling most of the important infective and parasitic diseases, prospects are good for rapid reduction in mortality from these diseases. The resultant increase in survival of the population will bring new problems to the regions affected. These are the problems of the chronic noninfectious diseases with which the developed countries are now struggling.

Iwao M. Moriyama

[See alsoFood, article onworldproblems; Population; Publichealth.]

BIBLIOGRAPHY

Campbell, Hubert 1965 Changes in Mortality Trends: England and Wales, 1931-1961. U.S. National Center for Health Statistics, Vital and Health Statistics, Series 3, No. 3. Washington: Government Printing Office.

Demographic Yearbook 1961. 13th ed. 1961 New York: United Nations. → Special Topic: Mortality Statistics. Prepared by the Statistical Office of the United Nations in collaboration with the Department of Social Affairs.

Demographic Yearbook 1963. 15th ed. 1963 New York: United Nations. → Special Topic: Population Census Statistics II. Prepared by the Statistical Office of the United Nations in collaboration with the Department of Social Affairs.

Shapiro, S.; and Moriyama, I. M. 1963 International Trends in Infant Mortality and Their Implications for the United States. American Journal of Public Health and the Nation’s Health 53, no. 5:747-760.

The Ten Leading Causes of Death for Selected Countries in North America, Europe and Oceania, 1954-1956, 1964a World Health Organization, Rapport epidemiologique et demographique 17:54-112.

The Ten Leading Causes of Death for Selected Countries in Africa, South and Central America and Asia, 1954-1956, 1960, 1961. 1964k World Health Organization, Rapport epidemiologique et demographique 17: 118-152.

U.S. Dept. of Health, Education, and Welfare, Public Health Service, National Center for Health Statistics 1964a The Change in Mortality Trend in the United States, Prepared by Iwao M. Moriyama. National Center for Health Statistics, Series 3, No. 1. Washington: Government Printing Office.

U.S. Dept. of Health, Education, and Welfare, Public Health Service, National Center for Health Statistics 1964b Recent Mortality Trends in Chile. National Center for Health Statistics, Series 3, No. 2. Washington: Government Printing Office.

U.S. Dept. Of Health, Education, And Welfare, Public Health Service, National Center For Health Statistics 1965 Changes in Mortality Trends in England and Wales, 1931–1961. Prepared by H. Campbell. National Center for Health Statistics, Series 3, No. 3. Washington: Government Printing Office.

U.S. Dept. of Health, Education, and Welfare, Public Health Service, National Vital Satistics Division 1964 Vital Statistics of the United States 1962. Volume 2: Mortality. Part A. Washington: Government Printing Office.

mortality, mortality rate The death-rate, usually standardized by age and sex, to facilitate comparisons between areas and social groups. It provides a measure of health risks, improvements in the quality of health care, and the comparative overall health of different groups in the population. It is thus used as a reliable indicator of social and economic change, and of comparative standards of living, as well as by epidemiologists who are interested in monitoring the risk of death from infectious diseases and other causes. A variety of mortality rates are used, each with its own purpose, with the overall national death-rate used as the starting-point for comparisons between areas and social groups in a society.

The crude death-rate is the number of deaths in a year per 1000 population in a defined geographical area. In effect a refined version of the absolute number of deaths, this is not very informative, as so much depends on the sex-ratio and age-structure of a population. Crude death-rates can be multiplied by Area Comparability Factors to produce corrected rates which are comparable one with another and enable direct comparisons between areas. More commonly, age-standardized death-rates are calculated separately for men and women, to produce overall Standard Mortality Ratios (SMR) for each sex, or for both sexes combined, for a given area or social group. The SMR compares age-specific death-rates for a given area or social group with national average age-specific death-rates. It is computed as the actual or observed number of deaths in the group of interest, divided by the expected number of deaths, multiplied by 100. (The expected number of deaths is the number that would have occurred if age-specific death-rates in the group of interest were equal to the national averages for the year.) Age-specific crude death-rates and SMRs can also be calculated to identify the age-groups accounting for mortality rates above or below the national average. Five-year and ten-year age-bands are normally used, but broader bands are sometimes used for age-standardization calculations. Mortality rates are also calculated for specific causes of death, such as cholera, cancer, or suicide; and to monitor the control of infectious diseases, improvements in health care, or the social consequences of high unemployment.

Some mortality rates are already age-standardized. The infant mortality rate is the number of deaths within the first year of life divided by the number of live births in the same year times 1000. The neonatal mortality rate is the number of deaths within the first four weeks of life divided by the number of live births in the same year times 1000. The perinatal mortality rate is the number of still-births plus the number of deaths within the first week of life, divided by total births (still-births and live births) in the same year, again times 1000. The maternal mortality rate is the number of maternal deaths divided by total births times 1000. See also LIFE-TABLE; MORBIDITY STATISTICS.

mor·tal·i·ty / môrˈtalətē/ • n. (pl. -ties) 1. the state of being subject to death: the work is increasingly haunted by thoughts of mortality. 2. death, esp. on a large scale: the causes of mortality among infants and young children. ∎  (also mortality rate) the number of deaths in a given area or period, or from a particular cause: postoperative mortality was 90 percent for some operations.

Mortality. See Death and Dying; Life Expectancy.

mortality see vital statistics .

mortality See death rate.