U.S. Census Bureau

The seasonal factors are based on a short time series that may not have stable seasonal patterns.  As more estimates are added to the time series, large revisions in seasonal factors and consequently historical estimates may be observed.   Data users should exercise caution when drawing inferences based on the seasonally adjusted estimates. Unless otherwise specified, seasonally adjusted estimates are obtained using a direct seasonal adjustment at the published NAICS (North American Industry Classification System) level.