evidenced in a society's treatment of minority groups, such as indigenous peoples, immigrants and migrant workers, and of vulnerable groups, such as women, children, the elderly and the infirm. These factors influence not only the general sense of social well-being but also the health of individuals and groups. Multiple measurement approaches can maximize data accuracy; however, the cost of such measurements must be taken into account.

     Societies at different stages of development exhibit distinct epidemiological profiles. The prevalence of various causes of death, average life expectancy, disability-adjusted life years, infant and under-five mortality rates and maternal mortality rates all fluctuate in discernible patterns as the economic underpinnings of society change. For example, societies that depend on hunting and gathering typically have short average life expectancies and deaths due to accident or injury are more prevalent. Agrarian societies show a greater prevalence of death from infectious disease as the major cause of death, particularly among children. In industrial societies, death from cardiovascular disease is predominant, whereas in a service-based post industrial society, the major cause of death is cancer. In the societal form now emerging, it is expected that the predominant cause of death will be senescence-age-related disorders (Horiuchi, 1999).

     Such a typology is useful as a rough guide when examining the health statistics or "health profiles" of countries at different stages of development. They demonstrate the linkages between socioeconomic development and human health: the heavy burden of infectious disease in poor, predominantly agrarian countries; the double burden of both infectious and noncommunicable diseases in middle-income developing countries where basic sanitation, clean water and health care systems have already considerably reduced under-five and maternal mortality rates and thereby lengthened average life spans. However, great differences still exist in the health status of rural and urban population groups; and advanced industrialized economies, with aging populations and a predominance of "lifestyle" diseases often related to excessive consumption, inadequate physical activity and the use of tobacco.

     Health gains in recent decades are nowhere more evident than in the extension of life expectancy at birth from a global average of 46 years in 1950-55 to 65.4 years a half century later. This progression is expected to continue, reaching an estimated global average life expectancy of 75.1 years in the period 2045-2050 (UN, 2005a). These positive gains are also witnessed in the speed with which developing countries have narrowed the gap in life expectancy between more industrialized and less developed regions of the world, from a difference of 25 years in the period 1950-1955 to slightly over 12 years in 2000-2005 (UN, 2005b). This rapid improvement is due principally to greater access to clean water, sanitation, immunization, basic health services and education: all factors that have transformed the health profile of populations.

     While these average figures demonstrate considerable global progress, they also mask wide disparities at the local, national and regional levels. For example, for the past decade, largely due to the ravages of AIDS, life expectancy in Africa has been declining, reaching the current level of

45 years, more than 20 years lower than the global average. The gap in life expectancy between sub-Saharan Africa and the industrialized economies of Europe and North America in 2000 was wider than at any time since 1950 (World Bank, 2006a).

     Quality of life questions gain in importance as average life expectancy grows, and here too the gaps between richer and poorer countries and regions are evident. People living in developing countries not only have lower average life expectancies, but also spend a greater proportion of their lives in poor health, than do those in industrialized countries. More than 80% of the global years lived with disability occur in developing countries, and almost half occur in highmortality developing countries. Healthy life expectancy, that is, total life expectancy reduced by the time spent in less than full health due to disease or injury, ranges from a low of 41 years in sub-Saharan Africa to 71.4 years in Western Europe, with the proportion of lost healthy years ranging from 9% in Europe and the Western Pacific to 15% in Africa (WHO, 2005).

     Infectious disease has ceded its place to noncommunicable illnesses, such as heart disease, cancer and degenerative conditions, as the primary cause of mortality worldwide. Noncommunicable diseases accounted for about 60% of all deaths and 47% of the global burden of disease in 2002, and figures are expected to rise to 73% and 60% by 2020 (WHO, 2003b). Yet, once again, sub-Saharan Africa is the striking exception to the rule, since more than 60% of deaths in that region are attributable to infectious disease, with HIV/AIDS as the number one killer of adults aged 15-59 (WHO, 2003b). The resurgence of infectious disease, whether due to the growth of drug-resistant germs, as in tuberculosis, or the transmission to humans of viral pathogens of animal origin continue to pose health threats worldwide.

     Poverty, malnutrition and infectious disease take a terrible toll among the most vulnerable members of society. Of the 57 million deaths worldwide in 2002, 10.5 million were among children less than five years of age. More than 98% of those childhood deaths occurred in developing countries. The principal causes were peri-natal conditions, lower respiratory tract infections, diarrhea-related disease and malaria, with malnutrition contributing to all (WHO, 2003b). Infections and parasitic diseases accounted for 60% of the total (WHO, 2003b). The prevalence of malnutrition and infectious disease among the young has important implications for the health and well-being of the population as a whole, since the functional consequences of ill health in early childhood are likely to be felt throughout life, affecting the individual's physical and mental development, susceptibility to disease and capacity for work. In rural areas, in particular, where much work requires sustained physical effort, lack of strength and endurance can lower labor capacity, productivity and earnings. Much of the burden of death as a result of malnutrition is attributable to moderate, rather than severe undernutrition (Caulfield et al., 2004). Young children with mild to moderate malnutrition had 2.2 times the risk of dying compared to their better nourished counterparts, and for those who were severely malnourished the risk of death was 6.8 times greater (Schroeder and Brown, 1994). Children from poor households had a significantly higher