United States. Bureau of Economic Analysis. "Gross Domestic Product, Second Quarter 2021 (Advance Estimate) and Annual Update : Historical Comparisons, BEA 21-36," Bureau of Economic Analysis (BEA) News Releases (July 29, 2021). https://fraser.stlouisfed.org/title/6148/item/604940/content/pdf/bea_newsreleases_20210729_historical, accessed on March 21, 2025.