The civilian labor force is the sum of employed and unemployed persons.
The series comes from the 'Current Population Survey (Household Survey)'.
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Civilian Labor Force - College Graduates - Doctoral Degree, 25 to 34 years [CGDDL2534], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/CGDDL2534/, June 2, 2015.