Michael A. Rees
University of Toledo
Department of Urology
3000 Arlington Avenue
Mail Stop 1091
Toledo, OH 43614
NBER Working Papers and Publications
|July 2012||The Need for (long) Chains in Kidney Exchange|
with Itai Ashlagi, David Gamarnik, Alvin E. Roth: w18202
It has been previously shown that for sufficiently large pools of patient-donor pairs, (almost) efficient kidney exchange can be achieved by using at most 3-way cycles, i.e. by using cycles among no more than 3 patient-donor pairs. However, as kidney exchange has grown in practice, cycles among n>3 pairs have proved useful, and long chains initiated by non-directed, altruistic donors have proven to be very effective. We explore why this is the case, both empirically and theoretically.
We provide an analytical model of exchange when there are many highly sensitized patients, and show that large cycles of exchange or long chains can significantly increase efficiency when the opportunities for exchange are sparse. As very large cycles of exchange cannot be used in practice, long non-simult...