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Bureau of Labor Statistics > Consumer Price Index > Methods > Seasonal Adjustment

Timeline of Seasonal Adjustment Methodological Changes

Date	Change
January 2021	With the publication of revised data from January 2016 through December 2020, additional intervention analysis seasonal adjustment was performed on seasonally adjusted series impacted by the COVID-19 pandemic.
January 2016	With the publication of data from January 2011 through December 2015, the Telephone services series changed from dependent adjustment to independent adjustment, replacing Wireless telephone services and Land-line telephone services as components of the seasonally adjusted All items index. This reduced the number of component series from 82 to 81.
January 2015	Introduction of X-13-ARIMA-SEATS for seasonal adjustment of CPI series, including intervention analysis seasonal adjustment (IASA) for certain series.
January 2011	With the publication of data from January 2006 through December 2010, the Video and audio series and the Information technology, hardware and services series were changed from independently adjusted to dependently adjusted. This increased the seasonal components used in deriving seasonal movement of the All items index and 64 other lower level aggregations, from 73 for the publication of January 1998 through December 2005 data to 82 for the publication of seasonally adjusted data for January 2006 and later.
January 2002	The expenditure weights used to calculate the Consumer Price Index (CPI) were updated and the seasonally adjusted indexes for dependently adjusted series were revised from January 1987 through December 2001. BLS began using the same aggregation weights for unadjusted and seasonally adjusted CPI data. For more information, click here. Note: The expenditure weights used in calculating the Consumer Price Index are updated periodically. Updates occurred in 1940, 1953, 1964, 1978, 1987, and 1998. From 2002 on, updates have occurred every 2 years.
February 1998	The CPI replaced the X-11-ARIMA and RAMPS software with the X-12-ARIMA software for non-intervention analysis seasonal adjustment series. X-12-ARIMA had been introduced for IASA series a year earlier.
February 1997	The CPI replaced the X-11-ARIMA and RAMPS software with X-12-ARIMA for IASA series.
1994	BLS began using a 1988 updated version of X-11-ARIMA.
1989	Beginning of the use of intervention analysis seasonal adjustment techniques in conjunction with X-11-ARIMA software for the adjustment of CPI series. BLS also developed an extension of X-11 ARIMA to allow it to adjust more adequately for the effects of the presence or absence of religious holidays in the April survey reference period and of Labor Day in the September reference period.
1980	BLS began using X-11-ARIMA for most seasonal adjustment. X-11-ARIMA was developed by Statistics Canada and provided the option of using autoregressive integrated moving average modeling and forecasting techniques.
1977	The updated seasonal data at the end of 1977 replaced data from 1967 to 1977. BLS announced that subsequent annual updates would replace 5 years of seasonal data.
1967	The Bureau of the Census introduced "The X-11 Variant of the Census Method II Seasonal Adjustment Program", or X-11. In the early 1970s, BLS used the X-11 method with increasing frequency.
1966	BLS began publishing seasonally adjusted data using the BLS Seasonal Factor Method. Work had begun on seasonal factor methods at BLS in 1959.

Last Modified Date: February 8, 2021