Africans south of the Sahara, an area convulsed in wars and weakened by natural disasters, also suffer the broadest range of social and economic disadvantages, a United Nations survey says. The survey, the Human Development Report, examines the availability of schools, clean water and medical care, and whether people can play a role in politics. It began 10 years ago as an experiment to measure a nation's growth not by economic figures but by statistical profiles of its people and what they can expect from life.