Childhood underweight in Ethiopia: modelling non-linear risk factors and geographic hotspots using Bayesian geoadditive methods

Objectives: Underweight in children under 5 years of age is defined as a weight- for-age z-score (WAZ) of less than −2 standard deviations (−2SD) from the median of the World Health Organization (WHO) Child Growth Standards (CGS). This study examines the effect of socio-demographic covariates and geographi- cal covariates on underweight, as well as the flexible trends of metrical covariates, to identify communities at a high risk of underweight. Methods: This study utilized cross-sectional data on underweight from the 2016 Ethiopian Demographic and Health Survey (EDHS). A Bayesian geoaddi- tive Gaussian regression model was used to analyse a sample of 10,641 children. Appropriate prior distributions were established for the scale parameters in the models, and the inference was conducted within a fully Bayesian framework using Markov chain Monte Carlo (MCMC) simulation. Results: The results indicate that the effects of metrical covariates, such as child age, the mother’s body mass index (BMI), and maternal age, on underweight were non-linear. Specifically, the relationship between the mother’s BMI and her child’s underweight appears to be an inverted U-shape within the maternal BMI range between 12 and 50 kg/m2. Lower and higher maternal BMI are associated with more severe cases of underweight (as indicated by lower WAZ z-scores). There is also significant spatial heterogeneity, and based on inverse distance weighting (IDW) interpolation of predictive values, the western, central, and eastern parts of the country are hotspot areas for underweight children. Conclusion: Socio-demographic and community-based programmes should be comprehensively integrated into Ethiopian policy to combat childhood malnutrition.