Question
Why do the sum-of-states and sum-of-metro areas forecasts not match the U.S. forecast for the same concept?
Answer
States
There is no mechanism to force the sum of state-level forecasts to equal the forecasts that come from the U.S. macro model. Such a constraint would add a layer of complexity to the forecast process that could potentially produce counterintuitive results.
Moreover, the sum-of-state totals for many historical economic data series, including employment, do not add up to national estimates. State and U.S. data are often gathered from different samples or using different methods. Sum-of-state totals for top-line forecast variables such as GDP, employment, the unemployment rate, population, households, and housing permits, however, are routinely checked during the monthly forecasting process to ensure that differences with the U.S. forecasts remain within a reasonable range.
Metro areas
Metro areas constitute only a portion of U.S. geography and economy (i.e., most states have a "non-metro" portion), so sum-of-metros should not equal the U.S. value. The sum will however be close to the U.S. value, since economic activity is concentrated in metro areas. They account for 85% to 90% of the U.S. economy, but this share can change over time.
See also
Related Releases
U.S. MSA Alternative Scenarios
U.S. MSA Forecast
U.S. State Alternative Scenarios
U.S. State Forecast