The results of the 2018 comprehensive update of the National Income and Product Accounts released July 27, 2018, reflect the outcome of a comprehensive review of the source data and seasonal adjustment methods that are used in constructing all the quarterly GDP estimates. Based on this extensive review, BEA is confident that our first quarter estimates represent reliable signals of economic activity in the quarter and that we have successfully addressed residual seasonality in estimates of GDP and its components. We conducted additional analysis that expands on traditional seasonal adjustment. For instance, we introduced statistical tests that focus on a specific quarter’s growth relative to the other quarters of the year. None of these tests found statistically weak first quarters compared against other quarters in the GDP estimates that were revised in the comprehensive update.
BEA has examined the components of GDP and has not identified any specific, consistent component as a driver of weaker aggregate GDP growth in first quarters. For more information, see the August 2018 Survey of Current Business “Seasonal Adjustment in the National Income and Product Accounts: Results from the 2018 Comprehensive Update.”