Intro
Health status is both a determinant of population change, largely through population aging, and a consequence of population growth, with smaller family size associated with lower mortality, and of economic and social development. Studies of the interrelationship between demographic trends and health have typically focused on health as the independent or determining variable. Indeed, a population's health status influences all components of population change. In addition to the obvious direct effect of individual health status on mortality and morbidity, it has a direct impact on fertility, largely through improved child survival, but also through the biological capability of a sick woman to bear children. Processes such as screening potential migrants for disease are also mechanisms whereby health status exerts a direct impact on population change, and thus on population size and composition.
In contrast, demographic variables influence health through two interrelated phenomena. First, a population's size, composition by age and sex, and geographical distribution have a direct influence on overall health status. Age has a particularly marked effect on the pattern and extent of ill-health in populations because of the strong relationship between age and mortality and morbidity. Second, each of the dynamic processes influencing population size and growth, structure, and distribution, namely, fertility, mortality, and migration, will also affect health status. Thus, any discussion of disease control priorities and of the health system for delivering interventions requires an understanding of the demographic context and how it is changing.
This chapter begins by providing an overview of global population trends in each major region of the world and the current size and composition of the population. Given this volume's focus on the descriptive epidemiology of diseases, injuries, and risk factors, we then examine trends in mortality over the past decade in more detail as background against which the current assessment of the disease burden might be more usefully interpreted. This includes both an assessment of trends in age-specific mortality and summary measures of the age schedule of mortality, such as life expectancy and the probability of dying within certain age ranges, as well as a specific discussion of trends in the main causes of child mortality. The focus on child mortality is entirely appropriate because (a) the fact that at the end of the 20th century, we remained woefully ignorant of its levels, let alone its causes, is highlighted; (b) the reduction of child mortality should remain a priority for global health development efforts, and the moral imperative to do so remains as relevant today as it was 30 years ago, when efforts to improve child survival became increasingly organized and focused; and (c) the resulting emphasis by the global public health community on reducing child mortality has yielded vastly more epidemiological information that can be used to assess trends in levels and causes. Nevertheless, we argue later in the chapter that large and unacceptable uncertainties about trends in cause-specific child mortality rates persist, with important implications for program planning and evaluation.
