United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "April 1972," Business Conditions Digest (April 1972) : 52-53. https://fraser.stlouisfed.org/title/43/item/7565/toc/54926 , accessed on July 16, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "April 1972," Business Conditions Digest (April 1972) : 52-53. https://fraser.stlouisfed.org/title/43/item/7565/toc/54926 , accessed on July 16, 2024.