Inequalities in stunting among under-five children in Tanzania: decomposing the concentration indexes using demographic health surveys from 2004/5 to 2015/6

BACKGROUND: Child stunting is a global health concern. Stunting leads to several consequences on child survival, growth, and development. The absolute level of stunting has been decreasing in Tanzania from from 50% in 1991/92 to 34% in 2016 although the prevalence is still high (34%)Stunting varyies across socioeconomic determinants with a larger burden among the socioeconomic disadvantaged group. The reduction of inequalities in stunting is very crucial as we aim to reduce stunting to 28% by 2021 and hence attain zero malnutrition by 2030 under Sustainable Development Goal 2.2.This study aimed at determining the trend, contributing factors and changes of inequalities in stunting among children aged 3–59 months from 2004 to 2016. METHODS: Data were drawn from the Tanzania Demographic and Health Surveys. The concentration index (CIX) was used to quantify the magnitude of inequalities in stunting. The pooled Poisson regression model was used to determine the factors for stunting, decision criterion for significant determinants was at 5% level of significance. The CIX was decomposed using the Wagstaff and Watanabe decomposition methods., the percentage contribution of each factor to the toal concentration index was used to rank the factors for socioeconomic inequalities in stutning. RESULTS: Inequalities in stunting were significantly concentrated among the poor; evidenced by CIX = − 0.019 (p < 0.001) in 2004, − 0.018 (p < 0.001) in 2010 and − 0.0096 (p < 0.001) in 2015. There was insignificant decline in inequalities in stunting; the difference in CIX from 2004 to 2010 was 0.0015 (p = 0.7658), from 2010 to 2015/6 was − 0.0081 (p = 0.1145). The overall change in CIX from 2004 to 2015/6 was 0.00965 (p = 0.0538). Disparities in the distribution of wealth index (mean contribution > 84.7%) and maternal years of schooling (mean contribution > 22.4%) had positive impacts on the levels of inequalities in stunting for all surveyed years. Rural-urban differences reduced inequalities in stunting although the contribution changed over time. CONCLUSION: Inequalities in stunting declined, differentials in wealth index and maternal education had increased contribution to the levels of inequalities in stunting. Reducing stunting among the disadvantaged groups requires initiatives which should be embarked on the distribution of social services including maternal and reproductive education among women of reproductive age, water and health infrastructures in remote areas.