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The Transition Phenomenon

Over the next three decades patterns of disease will change profoundly worldwide with a rise of noncommunicable disease, including cancer, in the developing world. Collectively these changes are called the health transition. Worldwide, fertility and mortality decline together. This creates the first step, the demographic transition in which there is a transition from high mortality and fertility to low mortality and fertility. The process is essentially complete in high income countries and almost complete in China and Latin America. It is starting in SubSaharan Africa where fertility seems to be starting to decline. These demographic changes have dramatic effects on age distributions in developing countries. Now comes the epidemiologic transition. The population grows older and noncommunicable diseases like cancer become the main causes of ill health. The proportion of the world’s population over 65 years of age will increase from 4% in 1990 to 9% in 2030 (184 million to 678 million) and the burden of noncommunicable disease will increase sharply.

The phenomenon is illustrated here with burden of disease. To quantify the full loss of healthy life the World Bank with WHO developed the disability-adjusted life year (DALY) to measure the global burden of disease. It is calculated referable to 1990. Roughly, it has two components. The life years part is how many years of life are lost due to premature death from the disease. The disability-adjusted part reflects the probability of getting a disability, the duration of life lived with the disability, and the approximate severity of the disability in terms of activity restriction (analogous to the Karnovsky index in oncology). Thus the DALY measures total disease burden as the combination of premature mortality plus disability.

Source: Summarized and adapted from Murray CJL and Lopez AD Eds (1994) Global Comparative Assessments in the Health Sector. Disease Burden, Expenditures and Intervention Packages. World Health Organization, Geneva.

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