Algorithm & Rankings
How the Algorithm Works
How does the Match algorithm work?
The matching algorithm uses the applicant Rank Order Lists, the program Rank Order Lists, and the number of available positions at each program to find the best possible outcome for each participant.
The algorithm starts with an attempt to place an applicant into the program that is most preferred on the applicant's list. Each applicant's Rank Order List is traversed "downwards", from most preferred program to least preferred, until the first program is reached at which the applicant can be tentatively matched, or until the applicant's list of choices is exhausted. Each program accepts applicants "upwards" on its Rank Order List, continually removing less preferred matches in favor of more preferred applicants, until the program is matched to the most preferred applicants who wish to be matched to the program.
What is the best strategy for ranking?
In order to get your best possible result, you should rank your choices in order of your true preferences. Rank all applicants that you would be willing to accept. Do not rank any applicant that you would not want to be matched to your program, even if it was the only applicant available to you in the Match.
The algorithm is specifically designed to give each participant their best result if they rank their choices in order of true preference. Using any other strategy may cause you to get a worse result for your program. For example, if you decide to order your preferences by how highly you think an applicant will rank your program, you may not get the best possible result for your program.
How do I submit a Rank Order List?
Programs must submit and certify their Rank Order Lists online in the NMS Match System by the Rank Order List deadline. The Rankings User Guide includes information on how to:
- Add an applicant to your Rank Order List
- Delete an applicant from your Rank Order List
- Reorder an applicant on your Rank Order List
- Import your Rank Order List from a file
- Certify your Rank Order List
- Print your Rank Order List
Can I change my rankings after certifying my list?
Yes. Even if you have already certified a Rank Order List you can return at any time to make changes until the Rank Order List deadline.
If you make changes to a list after it has been certified, you simply have to certify the list again before the deadline in order for it to be used in the Match.Related Links:
What do I do if an applicant I want to rank is not included in the list of registered applicants?
If an applicant does not appear on the list, it means the applicant has not yet registered to participate in the Match. Contact the applicant and encourage them to register for the Match as soon as possible.
What do I do if I have no acceptable applicants to rank?
If a program has positions available to begin in 2021 that you would like to fill but has no acceptable applicants to rank, you should certify a Rank Order List with no ranks. Programs that certify no ranks in Phase I will be carried over automatically to offer their positions in Phase II. Do not withdraw the program from the Match if the program has positions available.Related Links:
Can I control the distribution of applicants with different characteristics that might match with my program?
Yes. It is possible within the matching algorithm to attempt to recruit a particular distribution or "mix" of applicants based on specific applicant characteristics, such as language fluency or location of residence. To accomplish this, you use the Multiple List feature offered in the Match.Related Links:
Can I revert unfilled positions between Rank Order Lists in Phase II?
Requests to revert unfilled positions from one Rank Order List to another are accepted only for Phase I of the Match. This option is not available to programs in Phase II of the Match.
- What do I do if I have no acceptable applicants to rank?