United States. Bureau of Labor Statistics. "Nonfarm Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 2001 [Preliminary]," Productivity and Costs (August 7, 2001) : 13-13. https://fraser.stlouisfed.org/title/131/item/55964/toc/445980 , accessed on March 28, 2024.