According to the United Nations, the population of sub-Saharan Africa should more than double by 2050. But statistical data are scarce and do not give a clear picture of trends or factors of change. To make up for this lack of information, demographic surveillance systems (DSS) have been set up in spe-cific regions. Using examples of demographic surveillance projects in Senegal run by researchers of the Institut national d'études démographiques (INED) and the Institut de recherche pour le développement (IRD), Emmanuelle Guyavarch explains how they function and why they are useful to researchers.

Researchers have developed demographic surveillance systems in several specific regions of Africa. Their purpose is to provide accurate local data, in addition to that of national censuses and surveys, with a view to understanding the mechanisms behind demogra-phic and health trends. This is notably the case in Senegal, where three rural populations have been observed for several decades. The research findings obtained have led to a downward adjustment of WHO maternal mortality estimates for the country and have shed new light on the causes of maternal death. They have also shown that the very slow overall diffusion of modern contraception is not the consequence of cultu-ral resistance: when contraception is made available by strongly motivated health personnel, it can spread very rapidly, even in economically disadvantaged rural areas.

• Long-term observation of villages groups
• How can maternal mortality be reduced?
• Obstacles to the spread of contraception in Africa
• Box 1 : The demographic surveillance method used in Senegal