United States. Bureau of Economic Analysis. "Gross Domestic Product, 4th Quarter and Year 2020 (Second Estimate) : Technical Note, BEA 21-06," Bureau of Economic Analysis (BEA) News Releases (February 25, 2021). https://fraser.stlouisfed.org/title/6148/item/600711/content/pdf/bea_newsreleases_20210225_technote, accessed on March 21, 2025.