United States. Bureau of Labor Statistics. Division of Occupational Outlook and United States. Department of Labor. Manpower Administration. Occupational Employment Patterns for 1960 and 1975 : Bulletin of the United States Bureau of Labor Statistics, No. 1599 , Washington: For sale by the Supt. of Docs., U.S. Govt. Print. Off., December 1968, https://fraser.stlouisfed.org/title/4941, accessed on February 12, 2025.