The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNU03025670
Source: US. Bureau of Labor Statistics
Release: Employment Situation
US. Bureau of Labor Statistics, Persons Unemployed 15 weeks or longer, as a percent of the civilian labor force [U1RATENSA], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/U1RATENSA/, September 4, 2015.