Official population estimates can be produced using a variety of data sources and methods. These range from the direct extraction of information from continuously updated population registers to procedures for updating the status of a population enumerated previously in a periodic census. Additional sources and techniques involve the use of sample surveys or complementary sources of headcount statistics for specific age groups (e.g., immunization records, school enrollment statistics, electoral roll data). In all cases, the objective is to derive regular (typically annual) time series of the estimated size of a population classified by age and sex. Some methods and data sources are considered preferable, as they are more likely to produce internally consistent and reliable estimates. In all cases, the data and methods used to produce population estimates should be clearly documented and made readily available to data users. These metadata are essential for interpreting properly and for assessing the accuracy and reliability of population estimates and their suitability for informing policy formulation and implementation at the national level. Access to such metadata is especially important if population estimates are being used for comparative purposes at the global level.
This paper offers a concise review of the methods that are commonly used by national statistical offices to produce annual time series of population estimates by age and sex. These methods depend on the availability of two essential components: an initial population count and a method of time adjustment. Both components play a crucial role in determining the overall quality of a set of population estimates. The paper formulates specific recommendations concerning best practices for the production of official population estimates. Drawing on information from various sources used by the United Nations to produce its biennial edition of global population estimates, the World Population Prospects, the paper also provides (in the appendix) an overview of data availability and current practices in the production of official population estimates around the world.