Mortality Rates

Mortality refers to the incidence of death per 1,000 people among a given population and is essentially the same as the crude death rate; therefore, it is closely linked to life expectancy. Mortality should not be confused with morbidity, which is the incidence or prevalence of a given disease. Demographers typically rely on age- and sex-specific mortality rates, which measure the number of deaths of a given 5-year age group of males or females. Mortality rates vary considerably across the life cycle depending on the particular social circumstances in which people live. Typically, mortality rates tend to be relatively high for infants (especially in economically underdeveloped societies), tend to be low for children and young adults, and then rise steadily as people enter middle age, rising dramatically in old age. However, mortality is a complex phenomenon with multiple demographic, economic, sociological, psychological, cultural, and geographic dimensions.

Like fertility, mortality is a reflection of both biological circumstances (e.g., genetics, diet) and socioenvironmental context. The causes of mortality vary greatly among societies (as well as within them). Infant mortality rates (number of deaths of babies [less than 1 year old] per 1,000 infants) are an important measure of a society's health because infants are the most vulnerable members of any society. Typically, infant mortality rates are high in preindustrial societies both historically and currently; for example, in much of sub-Saharan Africa, infant mortality rates exceed 120 per 1,000 babies.

In preindustrial social contexts, the leading causes of mortality generally are infectious bacterial diseases (and, to a lesser extent, viral diseases), including respiratory infections (e.g., pneumonia), diarrheal diseases, cholera, malaria, tuberculosis, and measles; today, that list also includes acquired immunodeficiency syndrome (AIDS). Many of these are water-borne diseases. Thus, mortality rates in much of the developing world (Latin America, Africa, the Middle East, and Asia [excluding Japan]) tend to exceed 20 deaths per 1,000 people annually.

As societies industrialize, the mechanization of agriculture and the corresponding lower price of food tend to improve diets and thus lower mortality rates and raise life expectancies. Improved public health measures (particularly clean drinking water) and access to healthcare are also important. Thus, mortality rates in Europe, Japan, and North America generally are less than 7 deaths per 1,000 people annually. These changes are an integral part of the demographic transition.

Moreover, the decline in mortality rates is accompanied by a shift in the causes of mortality, a phenomenon often called the epidemiological transition. Essentially, mortality in economically advanced societies tends to result from environmental and behavioral causes, including smoking- and alcohol-related deaths, which produce proximate causes of death such as heart disease, strokes, and various forms of cancer. Excluding the middle-aged and elderly, other important causes include automobile accidents, homicide, suicide, and household accidents.