I am now studying the Spence's job market model using both signaling and screening.
It turns out that, when a worker's reservation value = 0 (she can get 0 if she does not get employed), then both pooling and separating equilibria always exist in signaling. However, in screening, pooling equilibrium does not exist, and the range for separating is also narrower than in signaling.
Why is that so? Does it have anything to do with the refinements such as intuition criterion?
Is it true that screening will always be stricter than signaling?
(Sorry for being verbose - still quite new to this area and do not know how to describe the problem easily.)
(Reference: The question is discussed in the 13th chapter of MWG's textbook.)