The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU01000060
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Civilian Labor Force Level: 25 to 54 years [LNU01000060], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNU01000060/, August 3, 2015.