Although disability has been the area of concern in the domain
of such disciplines as social welfare and public health, the serious
concern on the demography of disability as an important research subject
has emerged only recently. In the less developed countries where most of
the world popUlation lives, the rapid decline in mortality with little
reduction in fertility, under the conditions of underdevelopment,
nutritional deficiencies, insufficient coverage for health, inadequate
sanitation and safe water facilities, has been contributing to the
increasing number of disabled persons. This is because the availability
of modern medicine, even to an inadequate extent, has contributed to the
reduction in mortality, but many of those who survive become permanently
disabled. Apart from the differences in data collection systems in
different countries and the problems associated with such approaches,
the variations in prevalence of disability are partly attributed to such
factors as differential chronic and infectious disease patterns;
differential life expectancy; the age structure of populations and
population composition; differential nutritional status; differential
rates of exposure to environmental, occupational and traffic hazards;
and variations in public health practice [United Nations. (1990)]. In
developed countries where the increase in life expectancy had started to
occur earlier than the developing countries, the decline in fertility
led to the growing proportions of the elderly in their population. As
the proportion of the elderly popUlation in the total population gets
larger the proportion of the disabled become conspicuous. This is
because in both developed and deVeloping countries the age structure of
the disabled popUlation is predominantly elderly in comparison to the
overall population age structure. It has been observed that in such
developed countries where the ageing process has gone furthest, the
number of disabled persons have increased rapidly. [Okoliski
(1986).]