The effects of the change in the NRMP matching algorithm. National Resident Matching Program
A. E. Roth and E. Peranson
Department of Economics, University of Pittsburgh, Pa 15260, USA. alroth+@pitt.edu
CONTEXT: Following 2 years of heated controversy about the resident match,
the National Resident Matching Program (NRMP) recently voted to replace the
existing matching algorithm with a newly designed applicant-proposing
algorithm. OBJECTIVE: To design an applicant-proposing algorithm for the
match and compare it with the existing NRMP algorithm to determine how many
applicants and residency programs could be expected to receive better or
worse matches from the 2 algorithms, how the different algorithms influence
the opportunity for strategic behavior, and what advice can be given to
participants. DESIGN: Computational experiments compared the newly designed
applicant-proposing algorithm with the existing NRMP algorithm on the rank
order lists (ROLs) submitted by all applicants and residency programs in
the 1987 and 1993 through 1996 NRMP matches. RESULTS: Differences in the
matchings produced by the 2 algorithms are small: fewer than 1 in 1000
applicants would have received a different match. Most (but not all) of the
few applicants who are matched to different positions by the 2 algorithms
do better when the applicant-proposing algorithm is used; the opposite is
true for programs. Opportunities for profitable strategic behavior are very
rare for both applicants and programs under either algorithm. With either
algorithm, both applicants and programs can be advised that trying to get a
preferred match by behaving strategically is far more likely to harm than
to help them. CONCLUSIONS: The existing NRMP algorithm and the newly
designed applicant-proposing algorithm perform similarly. Both algorithms
make it sensible for applicants and residency programs to arrange their
ROLs based solely on their preferences for possible matches. The choice of
algorithms will systematically affect the matches of only a small group of
applicants (<0.1%). The NRMP's recent decision to use the
applicant-proposing algorithm starting in 1998 reflects a judgment about
the impact of this difference on applicants and programs.
