ZMP's Revisited

Tyler Cowan, following up on last summer's discussion of Zero Marginal Product workers (ZMP's, as he calls them), offers a proof point:

People unemployed over 6 months rose by a whopping 361k, 44% of all unemployed.

But again, unless each worker's productivity remains constant over time (it doesn't) it doesn't follow that the currently unemployed weren't productive when they were working. It could just be that the currently employed are working harder, which stands to reason.

ZMP's indeed. ZMV econ bloggers maybe.