Each July or August, the latest 3 complete calendar years are revised. At about 5 year intervals, the entire historical record is subject to revision. In 1988, BEA published a paper presenting the conceptual basis and framework of government transactions in the NIPA's, describing the presentation of the estimates, and detailing the sources and methods used to prepare estimates of Federal transactions and of State and local transactions. These major changes include the recognition of government investment and a new methodology for calculating depreciation, changes in the treatment of federal retirement programs, enterprise definition changes, changes in the treatment of Commodity Credit Corporation loans, deposit insurance changes, the redefinition of government sales and personal nontaxes, and new featured measures of chain output and prices. In addition, a summary methodology and list of source data covering all components was released in 1987, and has been updated for each annual and comprehensive revision.
Gross investment is broken down into structures and equipment.
Historial data for the full set of NIPA tables are available on BEA's website and are scheduled for publication.