With its 2018 comprehensive update of gross domestic product and related statistics, the Bureau of Economic Analysis completed a multiyear project to improve and modernize our seasonal adjustment practices.
This effort identified and addressed instances of residual seasonality – seasonal patterns that remained in some data series after they had been seasonally adjusted to remove such patterns. The comprehensive update to the National Income and Product Accounts on July 27 applied these improvements to the historical time series. Testing of these updated estimates found no significant evidence of residual seasonality in nominal GDP, real GDP, or the GDP price index.
The seasonal adjustment project and its results are described in an article, “Seasonal Adjustment in the National Income and Product Accounts: Results from the 2018 Comprehensive Update,” published in the August Survey of Current Business.