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Seasonal Adjustment of Chained Dollars

Introduction

The Foreign Trade Division (FTD) of the U.S. Census Bureau (Census) adjusts data for inflation by calculating chained dollars at aggregate levels based on seasonally-adjusted value data and price indices published by the U.S. Bureau of Labor Statistics, using 2005 as a base year. The FTD calculates real (chained) dollar data by first calculating fixed weighted deflators for all import and export prices before applying a chaining process. This approach is based on methodology developed for the National Income and Product Accounts by the U.S. Bureau of Economic Analysis (BEA). Beginning in 2009, the BEA implemented an approach to seasonally adjust deflators that was used in calculating the final chain-weighted dollars to remove residual seasonality in their published data. After introducing the methodology, BEA continued their research and in 2011, they implemented an improved methodology for removing the residual seasonality in imports of petroleum by seasonally adjusting the quantity data used in calculating the deflator for the petroleum series. During this time, Census and BEA agreed to take a unified approach to producing seasonally adjusted chained dollars, since residual seasonality was also identified in the Census basis data, and to better ensure consistency between the adjustments published by both agencies. Starting with the January 2012 release, selected prices that were identified as demonstrating a seasonal pattern will now be adjusted before the chaining process.

Methodology for Adjusting Chained Dollar Data

For all prices other than import petroleum that were identified as having a seasonal pattern, deflator calculations will remain unchanged, but these deflators will now be seasonally adjusted, when eligible, prior to chaining. For import petroleum, a new procedure is being introduced to calculate a price for each of the four import petroleum 5-digit end-use codes using seasonally adjusted data. An adjusted unit price is then calculated by dividing the seasonally adjusted value by the seasonally adjusted quantity. The unit price is divided by the rebase value to produce a seasonally adjusted fixed weighted deflator. These individual deflators are applied to each of the four petroleum end-use series, and the resulting fixed-weighted constant dollars are summed prior to creating one petroleum chained dollar series. The resulting data in either process will be seasonally adjusted chained dollar data.

Data Impacted by Methodological Changes

For the January 2012 release, revisions will be applied to 2010 and 2011 and be reflected in Exhibit 10 and 11 in the FT900. Revised 2010 data for Exhibit 10 are available in our Historical Series Real dollars (2005 chain-weighted dollars) table at http://www.census.gov/foreign-trade/statistics/historical/.

If you have any questions or need additional information, please contact the U.S. Census Bureau’s Data Dissemination Branch on (301) 763-2311 or at ftd.data.dissemination@census.gov.

Frequently Asked Questions


Source: U.S. Census Bureau | Foreign Trade | ftdwebmaster@census.gov |  Last Revised: March 09, 2012