Is fertility at replacement level in Ouagadougou, Burkina Faso? Assessing the impact of migrations

Fertility remains high in Burkina Faso as a whole, but the fertility transition is well advanced in the capital city, Ouagadougou. Formal neighbourhoods, in the centre of the city, are surrounded by informal areas devoid of public services. Migrants from the countryside, less educated women, and poor families more often live in informal areas. A Health and Demographic Surveillance System (HDSS) has been settled in 2008 at the periphery of the city. The city appears to be very heterogeneous in terms of fertility: the total fertility rate (TFR) is 1.8 children per woman in the formal areas followed, as against 3.5 in informal areas.
Composition effects and differences in fertility preferences and unmet needs for family planning are not sufficient to explain this large gap, which may be due, at least partially, to an artefact. Migration to the city and, even more, migration from formal areas to informal areas, seem to be highly related to fertility behaviour, so that TFRs may be biased by selective migrations. Our aim in this paper is to model jointly migrations and fertility in order to check whether selective migrations could explain these differences (and especially the low fertility level in the formal areas).