GILLES PISON, ANNABEL DESGRÉES DU LOÛ, AND ANDRÉ LANGANEY
The Bandafassi Study was initiated in 1970 as a research project on population genetics. Its objectives were to describe the genetic structure of an African population, to measure the genetic micro-differentiation between subgroups of this population (e.g. villages, lineages), and to examine which mechanisms were the more important ones: genetic selection, genetic drift, founder effects, marriage patterns, or past history of migrations. Information would be gathered from census, genealogies, and blood types. The population chosen for the study was the Mandenka Niokholonko, a small population of about 1,000 in the département of Kedougou in Eastern Senegal. The existence of a larger multidisciplinary project of the Musée de l'Homme of Paris for studying the entire populations of this department made the choice easy.
A further objective (both genetic and demographic) of the project was to measure directly the selective effects of particular genes, such as that responsible for drepanocytosis (gene S). Survival rates had to be estimated and differences according to the phenotypes of the persons examined. Such measures needed the follow-up of persons with known phenotypes over a period of several years. It was decided to follow the whole population and regularly to collect demographic information on births, deaths, marriages, and migrations.
The demographic surveillance initiated in 1970 in the Mandenka Niokholonko population was extended to the rest of the population of the Bandafassi area in two stages: in 1975, twenty-four villages, about 4,000 persons, were added, increasing the population under study to about 5,000; and in 1980, eight more villages, about 2,000 persons, were added, increasing the population to about 7,000. In 1984 the use of verbal autopsies (questionnaires) was also introduced to improve information on causes of deaths. Obtaining accurate demographic data, and studying levels, trends, and factors of child mortality, rapidly became a major objective along with genetic data collections.