United States. Bureau of Labor Statistics. "Footnotes," in United States. Bureau of Labor Statistics. "Private Business, Nonfarm Business, and Manufacturing Sectors : Third Quarter 1981," Productivity and Costs (October 29, 1981) : 12-12. https://fraser.stlouisfed.org/title/131/item/55904/toc/486643 , accessed on April 18, 2024.