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Investigating Residual Seasonality in Final Real Dollar Foreign Trade Series

Keywords: export, import, inflation, price deflator, seasonal adjustment, time series

The U.S. Census Bureau and the U.S. Bureau of Economic Analysis (BEA) publish official merchandise trade statistics. Price deflators are applied to the seasonally adjusted data; these values are then summarized into composite groups and chain-weighted. In recent years, the agencies have seen indications of residual seasonality in the final chain-weighted imports of petroleum values, although the diagnostic statistics for the various components do not provide strong evidence of seasonality. The Census Bureau and the BEA have differing approaches to calculating the final published series, and each agency performed analysis performed analysis to determine whether residual seasonality was in fact present and to find the best method of removing the seasonality. This paper provides details of the Census Bureau's analysis that focused primarily on petroleum data but included other commodity groups as well.