United States. Bureau of Labor Statistics. "Nonfarm Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1990 [Preliminary]," Productivity and Costs (August 6, 1990) : 15-15. https://fraser.stlouisfed.org/title/131/item/55912/toc/460504 , accessed on April 23, 2024.