United States. Bureau of Labor Statistics. "Nonfinancial Corporations - Appendix - Annual Data," in United States. Bureau of Labor Statistics. "Second Quarter 1989 [Preliminary]," Productivity and Costs (August 3, 1989) : 25-25. https://fraser.stlouisfed.org/title/131/item/55907/toc/457649 , accessed on March 28, 2024.