United States. Bureau of Labor Statistics. "Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1999 [Preliminary]," Productivity and Costs (August 5, 1999) : 12-12. https://fraser.stlouisfed.org/title/131/item/55966/toc/440574 , accessed on April 24, 2024.