United States. Bureau of Labor Statistics. "Business Sector," in United States. Bureau of Labor Statistics. "First Quarter 1991 [Revised] : Business, Nonfarm Business, Manufacturing, and Nonfinancial Corporations," Productivity and Costs (June 5, 1991) : 8-8. https://fraser.stlouisfed.org/title/131/item/55755/toc/462896 , accessed on April 19, 2024.