Sources:

1. Economic Report of the President: 2011 Report Spreadsheet Tables, B-46. Employees on nonagricultural payrolls, by major industry, 1965-2010, U.S. Government Printing Office [1] (12/29/2011)
2. Economic Report of the President: 2011 Report Spreadsheet Tables, B-35. Civilian population and labor force, 1929-2010, U.S. Government Printing Office [2] (12/29/2011)
3. Economic Report of the President: 2001 Report Spreadsheet Tables, B-46. Employees on nonagricultural payrolls, by major industry, 1950-2000, U.S. Government Printing Office [3] (12/29/2011)
4. Historical statistics of the United States, colonial times to 1970, Volume 1, Chapter D, Labor Force (Series D 1-682), U.S. Bureau of the Census, 1975 [4] (12/29/2011)