United States. Bureau of Economic Analysis. "National Income and Product Accounts | Gross Domestic Product: Second Quarter 2018 (Advance Estimate) | Comprehensive Update: 1929 Through First Quarter 2018 : Technical Note, BEA 18-37," Bureau of Economic Analysis (BEA) News Releases (July 27, 2018). https://fraser.stlouisfed.org/title/6148/item/602645/content/pdf/bea_newsreleases_20180727_technical-note, accessed on March 22, 2025.