The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU02032192
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Employment Level: Nonagriculture, Self-employed Workers, Unincorporated [LNU02032192], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU02032192/, July 2, 2015.