Lebergott's data on unemployment counts those working in New Deal stimulus programs as unemployed.
That's right. They went to work everyday, building things, painting murals -- whatever, but Lebergott refused to count them, saying:
This contrasts sharply, for example, with the German practice during the 1930′s when persons in the labor-force camps were classed as employed, and Soviet practice which includes employment in labor camps, if it includes it at all, as employment.
Robert Waldman renders it thus:
Lebergott assertst that it is reasonable to considert the WPA to be essnetially the same as Buchenwald, Dachau and the gulag (I am not exaggerating at all).
Lebergott's data series is, of course, beloved of right wing regressives who want to bend reality to their own warped vision.
For context and more, see Delong.
Waldman's legitimately impassioned comment appears here.