United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "April 1971," Business Conditions Digest (April 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7553/toc/368698 , accessed on May 13, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "April 1971," Business Conditions Digest (April 1971) : 86-87. https://fraser.stlouisfed.org/title/43/item/7553/toc/368698 , accessed on May 13, 2024.