United States. Bureau of Labor Statistics. "Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1993 [Revised]," Productivity and Costs (September 9, 1993) : 12-12. https://fraser.stlouisfed.org/title/131/item/55985/toc/469722 , accessed on April 19, 2024.