United States. Bureau of Labor Statistics. "Nonfinancial Corporations," in United States. Bureau of Labor Statistics. "Fourth Quarter and Annual Averages 1990 for Business, Nonfarm Business, and Manufacturing and 1990 Annual Averages for Nonfinancial Corporations," Productivity and Costs (March 6, 1991) : 13-13. https://fraser.stlouisfed.org/title/131/item/55753/toc/462232 , accessed on April 18, 2024.