Matching ProcessThe key to understanding the matching process is the concept of 'tentative acceptance'. The process is an 'applicant-proposing' one; this means that it is driven by the applicants' requests for placement. At first, all acceptances are tentative. As programs receive more requests, they will retain only those applicants they consider most desirable.
The Matching Program's role is that of an intermediary, executing binding instructions. The outcome is pre-determined by the rank lists of programs and applicants. At no point can this outcome be modified by a judgment or bias on the part of the intermediary, nor is there any element of chance.
In the following example, ten applicants (1-10) compete for eight positions offered by four programs (A-D, offering 3, 2, 2 and 1 positions respectively).
Initially, each applicant requests placement in his/her preferred program.
In the next round, the rejected applicants (3, 5 and 10) request placement at their next choice. Most of these requests will create a cascade of further reactions and requests.
At this point the matching process ends, with 2 and 5 remaining unmatched. That at least two applicants would remain unmatched is predictable, since there were ten applicants for eight positions. Note that the matched applicants are always matched to the highest program on their list that was willing to accept them. Programs retained their preferred applicants but usually did not get only their top choices. Applicants who do not match were presented for consideration to all the programs on their list.