Statistical Comparison of Fertility Rate Determinants Between Northern and Southern Nigeria Using the 2018 NDHS Microdata

The persistent North-South fertility differential in Nigeria, with northern total fertility rates approximately three children higher than southern rates, demands rigorous multivariate statistical analysis of its determinants using large-scale survey microdata to inform population policy. This study statistically compares fertility rate determinants between northern (North West, North East, North Central) and southern (South West, South East, South South) Nigeria using individual-level 2018 NDHS microdata for 41,821 women aged 15 to 49. Negative binomial regression modelled children ever born as the fertility outcome for the full sample and separately by region. Interaction terms tested differential effects of covariates by region. Blinder-Oaxaca decomposition quantified the explained (characteristics) and unexplained (coefficients) components of the North-South fertility differential. The mean children ever born was 4.8 in the North versus 3.2 in the South. Blinder-Oaxaca decomposition showed that 54 percent of the differential was explained by differences in observed characteristics, principally education (32 percent of explained gap) and contraceptive use (28 percent). Unexplained differences accounted for 46 percent, reflecting differential behavioural responses to the same characteristics. Negative binomial coefficients for female education showed significantly stronger fertility-reducing effects in the South than North (interaction p = 0.004). The study provides statistically grounded decomposition evidence and recommends equity-focused girls' education and family planning interventions as the highest-leverage strategies for closing the North-South fertility gap. Keywords: fertility determinants, Blinder-Oaxaca decomposition, NDHS microdata, North-South Nigeria, negative binomial regression