Is "not in the labor force" the right category? Treating it that way will reduce unemployment numbers by reducing the counted population.
No matter what category you put these groups in, you will have an uncomfortable discrepancy similar, although to a lesser degree, of comparing apples to oranges. This is because prisoners are not identical with non-exsistant people nor are they identical to employed people.
Additionally, since military is considered employment, Europeans could boost employment just by expanding their military: as if unemployment is caused by a small military. I sense this is not the conclusion the authors would like.
So I too will bet that 10 years from now, European unemployment numbers will be higher than the US. My explanation: the counting techniques, prison ratios, relative world influence, military sizes as well as greater employment security will remain about the same.