United States. Bureau of Labor Statistics. "Selected Service-Providing and Mining Industries, 2005 : Selected Service-Providing and Mining Industries, 2005, USDL 07-0823,"
Productivity and Costs by Industry
(June 8, 2007).
https://fraser.stlouisfed.org/title/9618/item/703985/content/pdf/prin_20070608, accessed on June 11, 2026.