United States. Bureau of Labor Statistics. "Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1990 [Preliminary]," Productivity and Costs (August 6, 1990) : 14-14. https://fraser.stlouisfed.org/title/131/item/55912/toc/460490 , accessed on May 1, 2024.