At the global level, major inequalities are clear and persistent, write Schellenberg and Berhanu, inequalities by wealth, geographical location, sex of the child, and by the mother’s education are well described and tracked. In the era of the Sustainable Development Goals, with its aim to leave no-one behind, the disaggregation of health outcomes by ethnicity is timely and precise says the commentary.

“Results from the study strongly indicate that marked and major differences exist in child mortality by ethnic group in all countries with data available.”

Data on ethnicity are not available in many countries, and proxy indicators used can be highly questionable. Moreover, as the authors of this commentary highlight, ethnicity can be a sensitive topic and data are not collected partly for political, historical, and colonial reasons. They conclude by saying: “To understand and address ethnic differences in child mortality, this study could present the first step towards local, multidisciplinary research, leading to multisectoral action. To avoid a great new divergence and to ensure no on is left behind, immediate action is needed.”