United States. Bureau of Labor Statistics. "Total Private Nonagricultural Establishments," in United States. Bureau of Labor Statistics. "Employment and Earnings, United States, 1909-72 : Bulletin of the United States Bureau of Labor Statistics, No. 1312-9," Employment and Earnings, United States (1973) : 51-52. https://fraser.stlouisfed.org/title/189/item/5433/toc/338573 , accessed on April 30, 2024.