David Gamarnik

Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA 02139

E-Mail: EmailAddress: hidden: you can email any NBER-related person as first underscore last at nber dot org
Institutional Affiliation: Massachusetts Institute of Technology

NBER Working Papers and Publications

July 2012The Need for (long) Chains in Kidney Exchange
with Itai Ashlagi, Michael A. Rees, 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...

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