Within the framework of the biennial publication, World Population Prospects, the Population Division of the United Nations Department of Economic and Social Affairs (UN DESA) has been producing estimates and projections of populations by age and sex and other demographic indicators for several decades and for all countries or areas of the world. The information included in these datasets is used widely by the United Nations system, academia and civil society, including for the monitoring of indicators used to track progress towards the Sustainable Development Goals (SDGs). In recent years, Member States have requested international organizations to base their estimation processes on data reported by the national statistical authorities.
In reviewing different sets of official population estimates provided by Member States from various regions of the world and comparing them to estimates from World Population Prospects, this paper provides an overview of the challenges involved in producing consistent time series of population estimates by age and sex. At the same time, it promotes an understanding of some of the causes of discrepancy across different sets of population estimates, and showcases examples where observed population counts or reported estimates require some adjustments. The purpose is to foster a better understanding of data quality and to urge caution, among both data producers and users, not to accept or use all observed data or reported estimates at face value.