The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU02027714
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Employment Level: All industries Self-employed, unincorporated [LNU02027714], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU02027714/, July 29, 2015.