United States. Bureau of Labor Statistics. "Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1991 [Preliminary]," Productivity and Costs (August 6, 1991) : 14-14. https://fraser.stlouisfed.org/title/131/item/55815/toc/463206 , accessed on April 26, 2024.