United States. Bureau of Economic Analysis. "Gross Domestic Product by Industry: Second Quarter 2018 | Comprehensive Update: 1997 Through First Quarter 2018, BEA 18-58," Bureau of Economic Analysis (BEA) News Releases (November 1, 2018). https://fraser.stlouisfed.org/title/6148/item/602666, accessed on March 19, 2025.