United States. Bureau of Labor Statistics. "Business Sector - Appendix - Quarterly Data," in United States. Bureau of Labor Statistics. "Second Quarter 1988 [Preliminary]," Productivity and Costs (August 4, 1988) : 13-13. https://fraser.stlouisfed.org/title/131/item/55807/toc/454940 , accessed on April 27, 2024.