Hidden by national averages: Unveiling the complex dynamics of ethnic disparities in under-five survival across sub-Saharan Africa.

Under-five mortality in sub-Saharan Africa has declined markedly, yet ethnic gaps persist and may even widen despite overall gains. This study uses two consecutive rounds of Demographic and Health Surveys (2007-2022) from twelve countries to trace how child characteristics, maternal education, household wealth, and urban-rural residence drive ethnic differentials in child survival. Country-specific total births ranged from 23,109 to 127,545 per survey round. Employing survey-weighted quasi-Poisson models with person-year offsets and a sequential Shapley-value decomposition, the study estimates crude and adjusted rate ratios for pairwise ethnic comparisons. It predicts mortality rates under counterfactual socioeconomic conditions. Results show enduring disparities, for example, among the Luo versus the Kalenjin in Kenya (adjusted RR 2.15, 95 % CI 1.83-2.51) and the Hausa versus the Yoruba in Nigeria (adjusted RR 1.39, 95 % CI 1.22-1.56), with maternal education accounting for roughly one-quarter to one-third of inequality. At the same time, the role of household wealth varies by context. Sensitivity analyses examining administrative boundary effects revealed that geographic mediation accounts for 15.4 % of ethnic disparities in Ghana's centralized system and 35.1 % in Nigeria's decentralized federal structure, suggesting that apparent ethnic disparities substantially reflect differential healthcare access across administrative units rather than intrinsic cultural factors. In Ghana, targeted policies combining fee removal and culturally tailored maternal care have noticeably narrowed ethnic gaps. These findings underscore that eliminating preventable child deaths by 2030 requires interventions that address both the socioeconomic and cultural determinants of ethnic disadvantage.