United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1971," Business Conditions Digest (June 1971) : 95-97. https://fraser.stlouisfed.org/title/43/item/7555/toc/237511 , accessed on April 25, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1971," Business Conditions Digest (June 1971) : 95-97. https://fraser.stlouisfed.org/title/43/item/7555/toc/237511 , accessed on April 25, 2024.