United States. Bureau of Labor Statistics. "Footnotes," in United States. Bureau of Labor Statistics. "First Quarter 1990 [Revised] : Business, Nonfarm Business, Manufacturing, and Nonfinancial Corporations," Productivity and Costs (June 4, 1990) : 14-14. https://fraser.stlouisfed.org/title/131/item/55973/toc/460162 , accessed on May 9, 2024.