United States. Bureau of Labor Statistics. Occupational Employment in Selected Nonmanufacturing Industries: Transportation, Communications, Utilities, Trade, Educational Services, State and Local Government : Bulletin of the United States Bureau of Labor Statistics, No. 2284.
Washington, D. C.:
U.S. Dept. of Labor, Bureau of Labor Statistics,
December 1987, https://fraser.stlouisfed.org/title/5251,
accessed on January 14, 2026.