Revisiting the proximate determinants of fertility in Nigeria: does the method of estimation matter?

Latifat Ibisomi, African Population and Health Research Center (APHRC)

In view of the recent socio-economic changes that have taken place in Nigeria in the last couple of decades, we re-examined the proximate determinants of fertility in the country at large as well as by socio-demographic characteristics. The 1990, 1999 and 2003 Nigeria Demographic and Health Survey (NDHS) data sets of women aged 15-49 years were used in the analyses of this work. The Bongaarts et al 1984 framework for the proximate determinants of fertility and its Stover’s reformulation were used for this purpose as well as to examine the effect of recent changes in childbearing behaviours on the proximate determinants. The Bongaarts et al formulation used marriage while the Stover’s reformulation used recent sexual activity as factors governing exposure to intercourse. Although differences exist in the values of the proximate determinant indices in the two models, they both have similar results, which is that the index of postpartum insusceptibility has the most inhibiting effect on fertility in Nigeria. This is followed by the indices of marriage/sexual activity, contraception and sterility in that order. This order might however change in the near future, as the gaps within and between the determinants are quite close in many cases. The indices jointly reduced total fecundity by 12.46 births in the total sample of married women in 1990; 8.90 births in 1999 and 9.45 births in 2003 in the Bongaarts model while the indices reduced potential fertility by 17.69 births in the total sample of sexually active women in 1990; 16.06 births in 1999 and 16.50 births in 2003 in the Stover’s reformulation. Results further show that a huge percentage of sexual activity in Nigeria takes place within union. This could have accounted for the similar results found in the two formulations.