United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1981," Business Conditions Digest (June 1981) : 80-83. https://fraser.stlouisfed.org/title/43/item/7418/toc/412373 , accessed on April 19, 2024.
United States. Bureau of the Census. "Diffusion Indexes," in United States. Bureau of the Census. "June 1981," Business Conditions Digest (June 1981) : 80-83. https://fraser.stlouisfed.org/title/43/item/7418/toc/412373 , accessed on April 19, 2024.