Key Population Definitions:

Population estimate: An estimated figure for the current or past population at a particular date.
Population projection: A figure for the future population of an area, usually based on applying past demographic change to a current or previous estimate.
Constraining: Constraining is an explicit adjustment of a population estimate from one source used to ensure that it matches another source. It is used in the Department of Health estimates to ensure that population estimates from Family Health Services data match population figures from ONS for the stated year at some geographic level, usually local authority or strategic health authority and ultimately at a national level. It attempts to eliminate the effects on the estimate of list inflation and unregistered patients. GP relevant population: One of the PCT populations produced by the DoH. It is the population of patients registered with GPs from that PCT constrained to the ONS estimates or projections for the year in question. The process of constraining means that it differs from the registered population.
Responsible population: This is the population that a PCT is responsible for. It includes all patients registered with GP practices in the PCT plus persons living in the PCT who are not registered with a GP practice.
Standardisation: Standardisation removes effects due to differences in population structure and allows comparison between areas with different demographic characteristics. There are two types of standardisation: direct (usually shown as directly standardised rates) and indirect (usually shown as standardised ratios – e.g. SMRs).