United States. Bureau of Labor Statistics. "Business Sector," in United States. Bureau of Labor Statistics. "Private Business, Nonfarm Business, and Manufacturing Sectors : First Quarter 1981 (and Data for Nonfinancial Corporations, Fourth Quarter 1980)," Productivity and Costs (April 27, 1981) : 4-4. https://fraser.stlouisfed.org/title/131/item/55901/toc/437822 , accessed on March 28, 2024.