United States. Bureau of Economic Analysis. "U.S. International Trade in Goods and Services, December 2021 : Historical Comparisons, BEA 22-04, CB 22-16," Bureau of Economic Analysis (BEA) News Releases (February 8, 2022). https://fraser.stlouisfed.org/title/6148/item/610914/content/pdf/bea_newsreleases_20220208_historical, accessed on March 17, 2025.