Access to graduate medical training programs such as residencies is a competitive process known as the Match. Senior medical students usually begin the application process at the beginning of their (usually) fourth and final year in medical school. After they apply to programs, programs review applications and invite selected candidates for interviews held between October and February. After the interview period is over, students submit a rank-order list to a centralized matching service (currently the National Residency Matching Program, abbreviated NRMP) by February. Similarly, residency programs submit a list of their preferred applicants in rank order to this same service. The process is blinded, so neither applicant nor program will see each other's list. Aggregate program rankings can be found here, and are tabulated in real time based on applicants' anonymously submitted rank lists.
The two parties' lists are combined by an NRMP computer, which creates stable (a proxy for optimal) matches of residents to programs using an algorithm. On the third Thursday of March each year ( Match Day ) these results are announced in Match Day ceremonies at the nation's 155 U.S. medical schools. By entering the Match system, applicants are contractually obligated to go to the residency program at the institution to which they were matched. The same applies to the programs; they are obligated to take the applicants who matched into them.
On the Monday prior to Match Day, candidates find out from the NRMP if (but not where) they matched. If they have matched, they must wait until the Match Day (Thursday) to find out where. If they have not secured a position through the Match, the locations of remaining unfilled residency positions are released to unmatched applicants the following day. These applicants are given the opportunity to contact the programs about the open positions. This is what is known as The scramble. This frantic, loosely structured system forces soon-to-be medical school graduates to choose programs not on their original Match list. Occasionally and unfortunately, this sometimes requires students to choose entirely new specialties. The scramble is widely considered to be an unfavorable and highly stressful way of obtaining a residency position.
The USMLE or COMLEX score is just one of many factors considered by residency programs in selecting applicants. The median USMLE Step 1 scores for graduates of U.S. Medical Schools for various residencies are charted in Table 2 on page 5 of Charting Outcomes in the Match available a Third year core clerkship grades are also considered prominently.