United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "July 1971," Business Conditions Digest (July 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7556/toc/149261 , accessed on April 25, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "July 1971," Business Conditions Digest (July 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7556/toc/149261 , accessed on April 25, 2024.