Assortative matching, adverse selection, and group lending

This note reconsiders a theoretical result asserted to explain the success of group lending programs in LDCs. It has been claimed that if groups are allowed to form themselves, risky and safe borrowers will sort themselves into relatively homogenous groups. This "positive assortative matching" can be exploited by lenders to solve an adverse selection problem that would otherwise undermine the effectiveness of such lending programs. I show that the positive assortative matching result does not necessarily hold if earlier models are extended to incorporate dynamic incentives.