The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNS13000091
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Unemployment Level: 35 to 44 years [LNS13000091], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/LNS13000091/, September 3, 2015.