United States. Bureau of Labor Statistics. "New Producer Price Indexes for Computer Training - NAICS 611420," in United States. Bureau of Labor Statistics. "July 2007 (Corrected)," PPI Detailed Report (July 2007) : 10-10. https://fraser.stlouisfed.org/title/63/item/21860/toc/138977 , accessed on April 18, 2024.