United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "May 1969," Business Conditions Digest (May 1969) : 94-96. https://fraser.stlouisfed.org/title/43/item/7530/toc/303402 , accessed on April 27, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "May 1969," Business Conditions Digest (May 1969) : 94-96. https://fraser.stlouisfed.org/title/43/item/7530/toc/303402 , accessed on April 27, 2024.