United States. Bureau of Labor Statistics. Division of Construction and Public Employment and United States. Works Progress Administration. "West North Central Cities, Volume IV" in Salaries and Hours of Labor in Municipal Police Departments, July 1, 1938 : Bulletin of the United States Bureau of Labor Statistics, No. 685 (1941). https://fraser.stlouisfed.org/scribd/?item_id=494414&filepath=/files/docs/publications/bls/bls_0685-v4_1941.pdf&start_page=1, accessed on September 20, 2017.