The Census Bureau's Population Estimates Program (PEP) produces July 1 estimates for years after the last published decennial census (2000), as well as for past decades. Existing data series such as births, deaths, Federal tax returns, Medicare enrollment, and immigration, are used to update the decennial census base counts. POP estimates are used in Federal funding allocations, in setting the levels of national surveys, and in monitoring recent demographic changes. Related terms: Estimates base (Population Estimates Program), Population projections