This page provides details on the data used on this site.
Sources
The United States government maintains an integrated system of national economic accounts.
· National Income and Product Accounts (NIPAs): A set of economic accounts that provide detailed measures of the value and composition of national output and the incomes generated in the production of that output
· Industry accounts: Input-output (I-O) accounts, which trace the flow of goods and services among industries in the production process and which show the value added by each industry and the detailed commodity composition of national output, and GDP by industry accounts, which measure the contribution of each private industry and of government to GDP
· Regional accounts: Estimates of GDP by state, of state personal income, and of local area personal income
· International accounts: International transactions (balance of payments) accounts and the international investment position accounts
Measuring the Economy: A Primer on GDP and the National Income and Product Accounts (September 2007) PDF
A high-level introduction to the concepts behind the NIPAs, the sectors and accounts, and the derivations of the measures. Includes an appendix on accessing the NIPA estimates interactively.
MP-1: An Introduction to the National Income and Product Accounts (September 2007) PDF
A more detailed review of the NIPA accounts and how they are related to financial accounting statements.
A Guide to the National Income and Product Accounts of the United States (September 2006) PDF
A more detailed guide to the NIPAs. Includes appendixes on how indexes, chained measures, and component contributions are calculated.
NIPA Handbook: Concepts and Methods of the U.S. National Income and Product Accounts (ongoing) PDF
A detailed guide to the concepts, data sources, and estimating methods behind the NIPAs.
The Bureau of Labor Statistics prepares estimates of productivity for the U.S. economy (which are partially based on estimates of GDP).
The Federal Reserve Board prepares flow of funds accounts that record the value of tangible and financial assets acquired and the value of liabilities incurred throughout the U.S. economy, and the sources of the funds used to acquire the assets.
Time Units
All of the NIPA tables are annual, and most have quarterly versions. Only a few are monthly (primarily personal consumption).
The Federal Reserve data is usually monthly, although some series have other time frequencies, such as bi-weekly, weekly, or daily.
Revisions
The NIPAs are estimates that are revised over time. Much of the source data that BEA uses to prepare the estimates are part of statistical programs that provide, over time, more complete or otherwise better coverage—for example, monthly surveys that are superseded by an annual survey that is drawn from a larger sample or that collects more detailed information. Some uses of the NIPAs require frequent and immediately available estimates and others require consistent, long-term time series, so the BEA follows a release cycle where revised, update versions of the estimates are released. Each revision is referred to as a "vintage."
“Advance” estimates are released near the end of the first month after the end of the quarter. Most of these estimates are based on initial data from monthly surveys; where source data are not yet available, the estimates are generally based on previous trends and judgment. Advance estimates are not prepared for gross national product, gross domestic income, national income, corporate profits, and net interest because of a lag in the availability of source data.
“Second” (formerly known as "preliminary") and “third” (formerly known as "final") quarterly estimates are released near the end of the second and third months, respectively; these estimates incorporate new and revised data from the monthly surveys and other monthly and quarterly source data that have subsequently become available.
Annual revisions of the NIPAs are usually carried out each summer and cover the three previous calendar years. These estimates incorporate source data that are based on more extensive annual surveys, on annual data from other sources, and on later revisions to the monthly and quarterly source data. These revised NIPA estimates improve the quality of the picture of U.S. economic activity, though the overall picture is generally similar to that shown by the current quarterly estimates.
Comprehensive revisions are carried out at about five-year intervals and may result in revisions that extend back for many years. These estimates incorporate all of the best available source data, such as data from the quinquennial U.S. Economic Census. Comprehensive revisions also provide the opportunity to make definitional, statistical, and presentational changes that improve and modernize the accounts to keep pace with changes in the U.S. economy.
NIPA Tables
There are seven summary NIPA accounts that correspond to the seven economic sectors. There are more than 300 detailed NIPA tables (complete list). They are grouped in roughly the same order as the seven summary accounts. Table numbers are in the format “X.Y.Z.” where “X” indicates the NIPA table section, “Y” indicates the table number in the section, and “Z” indicates the type of estimate presented. For some tables, a letter suffix following the table number indicates that there are different versions of the table for different time periods.
The NIPA table sections are:
1. Domestic Product and Income
2. Personal Income and Outlays
3. Government Current Receipts and Expenditures
4. Foreign Transactions
5. Domestic Saving and Investment
6. Income and Employment by Industry
7. Supplemental Tables
8. Seasonally Unadjusted Estimates
These sections correspond to the summary account tables, except (a) there are no tables for the private enterprise sector (the private enterprise accounts, except for interest, can be found in the other tables; the total for the private enterprise sector, including interest, is only available annually), and (b) the last three table sections are not shown in the summary accounts.
Types of Estimates
Most of the NIPA estimates are presented in current or nominal dollars. Changes in current-dollar estimates measure the changes in the market values of goods or services that are produced or sold in the economy.
Changes in the market value for current-dollar measures may reflect a change in quantity, a change in price, or a combination of both. For many purposes, it is necessary to decompose these changes into price and quantity components.
Many NIPAs have estimates of changes in quantities and prices, expressed as indexes that provide information on the change from some reference period. The level of an index in any single period is not in itself meaningful. Instead, it is the relation of that index level to the index level in another period — that is, it is the change in the index over time — that is important. The reference period, for example the year 2000 for annual data, is set to 100. These are referred to as "chain-type" indexes.
Selected quantity index series are also expressed in monetary terms, called chained dollars. The index is scaled by setting the index in the reference period equal to the current-dollar level in the same period, and the change in the index in successive and previous periods is multiplied by the same current-dollar level of the reference period to form a time series in monetary terms. For most components of GDP, the chained-dollar estimates also provide rough approximations of their relative importance and of their contributions to real GDP growth for years close to the reference period. However, for some components—such as computers and other high-tech equipment with rapid growth in real sales and falling prices—chained-dollar levels (as distinct from chain-weighted indexes and percent changes) overstate the relative importance of such components to GDP growth.
In addition, chained-dollar values for the detailed GDP components will not necessarily sum to the chained-dollar estimate of GDP (or any intermediate aggregate) because the relative prices used as weights for any period other than the reference year differ from those used for the reference year. BEA provides a measure of the extent of such differences by showing a “residual” line on chained-dollar tables that indicates the difference between GDP (or other major aggregate) and the sum of the most detailed components in the table. For periods close to the reference year, when there usually has not been much change in the relative prices that are used as the weights for calculating the chain-type index, the residuals tend to be small, and the chained dollar estimates can be used to approximate the contributions to growth and to aggregate the detailed estimates.
For periods further from the reference year, the residual tends to become larger, and the chained-dollar estimates are less useful for analyses of contributions to growth. For this reason, BEA also shows contributions of major components to the percent change in real GDP (and to the percent change in other major aggregates) that use exact formulas for attributing growth. These are provided because the chained-dollar measures of components are not additive, and therefore, accurate measures of a component’s contribution to change cannot be derived from the chained-dollar measures.
BEA also prepares another price index, the implicit price deflator (IPD), which is calculated as the ratio of the current-dollar value to the corresponding chained-dollar value, multiplied by 100. The values of the IPD are very close to the values of the corresponding chain-type price index for all periods.
Two tables show the percentage shares of GDP and GDI that are accounted for by major components. These shares, which are calculated on a current-dollar basis, provide data users with an accurate measure of the size and importance of the components of GDP and GDI.
Each type of measure is provided in a separate table. The last digit of the table number identifies the type of measure. Not all tables have all measures.
1. Percent change from preceding period in real estimates (most at annual rates)
2. Contributions to percent change in real estimates
3. Real estimates, quantity indexes
4. Price indexes
5. Current dollars
6. Real estimates, chained dollars
7. Percent change from preceding period in prices
8. Contributions to percent change in prices
9. Implicit price deflators
10. Percentage shares of GDP
The tables that present current-dollar estimates, but not other types of estimates, use only the first two terms of the numbering system.
Seasonal Adjustment
Quarterly and monthly NIPA estimates are seasonally adjusted at the detailed series level when the series demonstrate statistically significant seasonal patterns. Seasonal adjustment removes from the time series the average effect of variations that normally occur at about the same time and in about the same magnitude each year — for example, weather and holidays. After seasonal adjustment, cyclical and other short term changes in the economy stand out more clearly.
Annual Rates
Quarterly and monthly NIPA estimates in current and chained dollars are presented at annual rates, which show the value that would be registered if the rate of activity measured for a quarter or a month were maintained for a full year. Annual rates are used so that periods of different lengths — for example, quarters and years — may be easily compared. These annual rates are determined simply by multiplying the estimated rate of activity by 4 (for quarterly data) or by 12 (for monthly data).
Seasonal adjustment and annual rates are usually show together. The units are labeled "SAAR."
Percent changes in the estimates are also expressed at annual rates. Calculating these changes requires a variant of the compound interest formula,
Imputations
[more detailed data available -- account detail, by state/industry/product. Link to list pdf.]
[how to look at data -- misleading curves, use of log; cycles; relationships; seasonality]
