United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1971," Business Conditions Digest (June 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7555/toc/237504 , accessed on March 29, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1971," Business Conditions Digest (June 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7555/toc/237504 , accessed on March 29, 2024.