United States. Bureau of Economic Analysis. "Gross Domestic Product (Third Estimate), Corporate Profits (Revised Estimate), and GDP by Industry, First Quarter 2021 : Technical Note, BEA 21-29," Bureau of Economic Analysis (BEA) News Releases (June 24, 2021). https://fraser.stlouisfed.org/title/6148/item/604396/content/pdf/bea_newsreleases_20210624_technote, accessed on March 19, 2025.