Each year with the release of the January CPI, seasonal adjustment factors are recalculated to reflect price movements from the just-completed calendar year. This routine annual recalculation may result in revisions to seasonally adjusted indexes for the previous 5 years. Recalculated seasonally adjusted indexes as well as recalculated seasonal adjustment factors for the period January 2017 through December 2021 were made available on Tuesday, February 8, 2022. The revised indexes and seasonal factors are available on this page.
In 2020, multiple PPI and CPI series measured extreme price movements as a result of the COVID-19 pandemic. For example, the unadjusted PPI and CPI for gasoline decreased 54.7 and 16.5 percent respectively in April 2020. Because the PPI and CPI use historical data to estimate seasonal patterns, extreme price movements in 2020 could have adversely affected seasonal adjustment. The PPI and CPI seasonal adjustment during the COVID-19 pandemic article explains the steps the BLS took to mitigate the effects of the COVID-19 pandemic on seasonally adjusted price indexes. In particular, it outlines how BLS greatly increased the scope of intervention modeling for both the PPI and CPI in 2021 and how this strategy was effective in mitigating the effects of the COVID-19 pandemic on seasonal adjustment. As a result of this increase in intervention work, revisions to the all items CPI and the PPI for final demand during the 2021 seasonal revision were similar in magnitude to pervious revisions.
The Consumer Price Index (CPI) produces both unadjusted and seasonally adjusted data. Seasonally adjusted data are computed using seasonal factors derived by the X-13ARIMA-SEATS Seasonal Adjustment Method. These factors are updated with the release of January data in February and reflect price movements from the previous calendar year. The new factors are used to revise the previous 5 years of seasonally adjusted data; older seasonally adjusted indexes are considered to be final.
Last Modified Date: May 3, 2022