About the data
The annual ONS mid-year estimates of the resident population of England and Wales are usually published about 12 months after the date they refer to. Although these official statistics are unrounded, they are estimates rather than counts and are subject to a degree of uncertainty. The initial release includes estimates for local authority (LA) areas and larger geographies. A second release provides estimates for smaller geographies about four months after the first.
Currently, these estimates are based on the census, which takes place every ten years. The estimates are updated each year using a cohort component method. This uses the most reliable available data sources to estimate components of population change. The three major components are natural change, migration, and special populations.
The estimates refer to the usually resident population, an internationally agreed definition. This includes only people who reside in a country for 12 months or more, with visitors and short-term migrants excluded. international migrants are usually resident if they intend to stay in England and Wales for more than 12 months.
For a few groups of people, the usual residence is defined using specific rules. For example, higher education students and schoolchildren studying away from home are considered usually resident at their term-time address, while members of the armed forces are usually resident at the address where they spend most of their time.
