United States. Bureau of Labor Statistics. "Nonfarm Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1988 [Preliminary]," Productivity and Costs (August 4, 1988) : 14-14. https://fraser.stlouisfed.org/title/131/item/55807/toc/454941 , accessed on April 27, 2024.