Revisions
The International Trade Division (ITD) of Statistics Canada produces monthly International Merchandise trade values, price indices and volume indices on both a Customs and Balance of Payments (BOP) basis. These figures are prepared under very tight deadlines and depend primarily on large volumes of administrative records received from the Canadian Border Services Agency and the United States Customs and Border Protection Agency. In accordance with the agreement on the exchange of import data, Canadian and United States international merchandise trade data are released simultaneously by Statistics Canada and the United States Census Bureau approximately 35 days after the end of the reference month.
In addition to being a closely watched indicator in its own right, merchandise trade data are a critical input to the System of National Accounts and BOP basis data are prepared in accordance with the System of National Accounts concepts, definitions, and revision schedule in mind. While the Customs data are available on the day of release, it is the seasonally adjusted BOP based data series, along with the associated price and volume indices, that are the focus of the monthly release in the Daily.
Factors influencing revisions include late receipt of import and export documentation, incorrect information on customs forms, replacement of estimates produced for the energy section with actual figures, changes in classification of merchandise based on more current information, and changes to seasonal adjustment factors. In general, merchandise trade data are revised on an ongoing basis for each month of the current year. Current year revisions are reflected in both the Customs and Balance of Payments based data.
The previous year's Customs data are revised with the release of the January and February reference months as well as on a quarterly basis. The previous two years of Customs based data are revised annually and are released in February with the December reference month. Previous year’s BOP based data are revised with the release of the January, February and March reference months. Revisions to BOP based data for the previous four years are released annually in June with the April reference month.
Seasonal Adjustment
Seasonal adjustment of Customs and BOP values and indices is performed at an aggregated commodity grouping level. Monthly fluctuations can occur as a result of weather patterns, roving holidays (such as Easter) and institutional factors (such as scheduled factory shut downs). In order to isolate turning points or trends in the basic data, it is necessary to eliminate this effect of seasonal movement. To remove seasonal fluctuations from time series, Statistics Canada uses the SAS® X12 procedure (SAS Institute Inc., 2010), and adaptation of the U.S. Census Bureau X-12-ARIMA Seasonal Adjustment program (U.S. Census Bureau, 2010). The seasonal adjustment process is applied following the Statistics Canada Quality Guidelines.
Revised data are available in the appropriate CANSIM tables.
Reference
SAS Institute Inc. (2010), “The X12 Procedure”, SAS 9.2 Documentation: SAS/ETS 9.22 User’s Guide, Cary, NC: SAS Institute Inc.
U.S. Census Bureau (2010), X-12-ARIMA Seasonal Adjustment Program, Version 0.3, Washington, DC.