Mortality Differentials, Socioeconomic
MORTALITY DIFFERENTIALS, SOCIOECONOMIC
Research on differential mortality generates answers to questions such as the following: To what extent are there within-country differences in mortality between subpopulations defined by area of residence, socioeconomic status, marital status, and other variables? What are the causes of such differences? How and why does the extent of the differences change in time and vary between countries?
The answers to these questions are important from a social and health policy perspective because mortality differentials are useful indicators of the health and well-being of population groups. Studies on differential mortality also contribute to the understanding of the determinants of mortality levels and trends in national populations. For epidemiologists cause-specific mortality differences provide clues to the etiology of diseases.
Research on differential mortality has long traditions. As early as 1901 the Danish researcher Harald Westergaard published a 700-page treatise that summarized the results of hundreds of studies carried out in the nineteenth century. The book by Evelyn M. Kitagawa and Philip M. Hauser published in 1973 is a classic American study on this topic.
This article discusses mortality differentials by socioeconomic status, racial/ethnic group, marital status, geographic area, and rural-urban division. The article focuses on developed countries. The data and research on less developed countries are relatively scarce and mainly concern infant and child mortality.
Mortality Differentials by Socioeconomic Status
Several indicators, such as occupational class, level of education, and income, have been used in studies of socioeconomic differentials in mortality. Information about these differentials usually is not available in regular statistics because the ordinary sources of mortality statistics do not include reliable information on the socioeconomic characteristics of deceased persons. Most knowledge about socioeconomic differences in mortality comes from studies for which data have been specifically collected for an analysis of socioeconomic differences.
Despite the measurement problems there is abundant evidence from different periods and countries showing that persons in lower socioeconomic positions die on average younger than do those in higher socioeconomic positions. For example, Eileen M. Crimmins and Yasuhito Saito (2001) estimated that the difference in life expectancy at age 30 between persons with 13 or more years of schooling and those with less than nine years was 6.7 years among white men and 3.8 years among white women in 1990 in the United States. Among African Americans these differences were, respectively, 11.8 years and 10.5 years.
Many hypotheses about the causes of socioeconomic mortality differences have been offered, but experts differ about their validity. Some hypotheses emphasize the causal effects of differences between classes in working and living conditions, health-related behaviors (e.g., smoking, alcohol use, diet), the prevalence of psychosocial stressors, or access to health services. According to other hypotheses, poor health and certain characteristics of individuals (e.g., social background and intelligence) may affect both their socioeconomic position and their risk of premature death.
Cross-national variation in the extent of socioeconomic differences in mortality in the 1980s was studied in a large project coordinated by John P. Machenbach and Anton E. Kunst from the Erasmus University Rotterdam (1997). Data for thirteen European countries and the United States were used. The mortality of men in manual occupations was higher than that of men in nonmanual occupations in all those countries. The relative excess mortality of the manual class was remarkably similar (ranging from 32% to 44%). However, larger differences were observed for France, the Czech Republic, and especially Hungary.
The results for mortality by cause of death showed that the mortality of manual workers was higher than that of nonmanual employees for nearly all the causes of death distinguished in the study. There was, however, an interesting exception: No class difference was found in mortality from ischemic (coronary) heart disease in France, Switzerland, Italy, and Spain. In Portugal mortality rates were higher in the nonmanual classes than in the manual classes. However, socioeconomic gradients in mortality from causes other than ischemic heart disease were steeper in southern European than in northern European countries.
Socioeconomic differences in mortality have widened in almost all the countries for which data are available, including the United States. The main reason for the increase has been a more rapid than average decline in mortality from cardiovascular diseases among persons with high socioeconomic status.
Differentials by Race/Ethnicity
Few countries report mortality differences by race or ethnicity, but in the United States the white-black division has been used as a standard classification for more than a hundred years. The life expectancy of the black population has always been lower, but the size of the difference has varied. It narrowed from 15.8 years in 1900 to 5.7 years in 1982, increased to7.1 years in 1993, and declined to 6.0 years in 1998. The increase in the gap from 1983 to 1993 was largely the result of increases in mortality among the black male population caused by HIV infection and homicide.
Since the 1990s more detailed classifications than the white-black dichotomy have been used. For example, Richard G. Rogers and colleagues (2000) studied mortality differences among adult Americans in the period 1989–1995 by using seven race/ethnicity groups. The age-and sex-adjusted excess mortality of African Americans compared to white Americans was found to be 41 percent, but after controlling for social and economic factors (education, income, employment status, and marital status) the excess mortality was only 17 percent. Sixty percent of the excess thus was due to the difference in the composition of the two groups. The mortality of Asian Americans was 31 percent lower than that of white Americans and remained 19 percent lower after controlling for nativity and social and economic factors. The four Hispanic groups distinguished in the study displayed varied mortality levels.
Hundreds of studies since the nineteenth century have shown that married persons live longer than do single, divorced, and widowed persons. One cause for the longer life of married persons is the selection of healthier than average persons into the married state. Selection also occurs on the basis of personal characteristics that affect the risk of death, such as level of education, psychological characteristics, and drinking habits. Another reason for the longer life of married persons is the protective effect of the married state associated with psychosocial factors (less stress and more social support), financial circumstances (more income and better housing conditions), and health behavior (healthier diet, less smoking and alcohol consumption). The adverse effects of divorce and loss of a spouse account for part of the excess mortality of divorced and widowed persons.
A comparative study of seventeen countries from the 1950s to the 1980s by Yuanreng Hu and Noreen Goldman (1990) showed that unmarried (single, divorced, and widowed) men of working age had a clear excess mortality (100% on average) compared to married men in all countries. In most countries divorced men had the highest death rates among the three unmarried groups. Unmarried women also had excess mortality compared with married women, but the excess was smaller (50% on average) than it was among men.
There is variation in the size of marital status differences between both countries and time periods. A general tendency has been an increase in the relative excess mortality of the unmarried groups. As shown by Tapani Valkonen (2002), this increase was particularly pronounced among elderly women in Western and Northern European countries as well as in Canada.
Geographic Differentials and Rural-Urban Differentials
Statistics on mortality for areas within countries, such as states, provinces, municipalities, and neighborhoods, usually show more or less systematic geographic variations. For example, life expectancy is several years higher in southern than in northern regions in many European countries, such as the United Kingdom, Russia, France, and the Scandinavian countries. In the United States there is a zone of low mortality in the north-central part of the country (e.g., Minnesota, North Dakota, and Iowa had life expectancies above 77 years in 1990) and a zone of high mortality in the southeastern region (e.g., Missouri, Louisiana, and South Carolina had life expectancies of 73.5 years or less).
Geographic differentials in mortality can be accounted for partly by differences in the composition of the population by occupational class, education, race/ethnicity, and other characteristics of individuals, but they are not due only to population composition. A large number of studies have shown associations between the level of mortality and a multitude of characteristics of areas, such as climate, mineral content of drinking water or soil, environmental pollution, quality of health services, dietary traditions, income inequality, and social cohesion. The causal interpretation of these results is, however, controversial.
Statistics on mortality by rural-urban division are available for relatively few countries. In the United States mortality is higher in urban than in rural areas. James S. House and colleagues (2000) have shown that this difference cannot be accounted for by differences in the socioeconomic and racial composition of the population. The age-adjusted mortality of city residents was found to be 60 percent higher than that of residents of small towns and rural areas and 40 percent higher than that of suburbanites after the effects of differences in population composition were adjusted for. In Russia and most other former socialist countries mortality is higher in rural than in urban areas. For the Western European countries the evidence is scarce, but it seems that rural-urban differences are small and that their direction varies from country to country.
The size and direction of the rural—urban mortality gap are determined by the balance of the influence of two factors. The higher average income and educational levels favor the urban areas, but the risks connected with urban life (environmental pollution, social stress, violence, smoking, and the use of alcohol and drugs) reduce the positive effects of higher living standards.
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