Matching Process
The 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.
- A receives requests from 2, 6 and 9; it tentatively accepts all
three.
- B receives requests from 4 and 10; it accepts 4, but did not list
10 as acceptable.
- C receives requests from 1, 3 and 7; it accepts 1 and 7, but rejects
3, since it has only two positions.
- D receives requests from 5 and 8; D is not interested in 5 and
accepts 8, even though it is its last choice.
PROGRAMS
|
|
| APPLICANTS
|
3
| 2
| 2
| 1
|
|
| <<< Number of positions available
|
A
| B
| C
| D
|
|
| 1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
| 9
| 10
|
(6)
| 7
| 4
| 1
|
|
| (C)
| (A)
| C
| (B)
| D
| (A)
| (C)
| (D)
| (A)
| B
|
10
| (4)
| (1)
| 4
|
|
| A
| D
| B
| A
| C
| C
| B
| A
| D
| D
|
4
| 6
| 6
| 7
|
|
| D
| B
| A
| D
| A
|
| A
| B
| C
| A
|
3
| 1
| (7)
| 10
|
|
| B
| C
| D
| C
|
|
| D
| C
|
| C
|
1
| 5
| 10
| 6
|
8
| 3
| 3
| 9
|
7
|
| 9
| (8)
|
(9)
|
| 2
|
|
5
|
(2)
|
|
|
|
|
|
|
|
| 10
|
| 5
|
|
| <<< These applicants were not listed.
|
Legend: (...) tentative acceptance; --- rejected
request
|
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.
- 3 requests B; B accepts.
- 5 requests C, but C is not interested. 5 now requests A; A considers
this an improvement and rejects 2. 2 now requests D, but D is not
interested, nor are B and C. 2's list is now exhausted, so 2 will
remain unmatched.
- 10 requests D; this is an improvement for D, so D rejects 8. 8
now requests A; A moves up again and rejects 5. Since 5's list is
now exhausted, 5 remains unmatched also.
PROGRAMS
|
|
| APPLICANTS
|
3
| 2
| 2
| 1
|
|
| <<< Number of positions available
|
A
| B
| C
| D
|
|
| 1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
| 9
| 10
|
[6]
| 7
| 4
| 1
|
|
| [C]
| (A)
| C
| [B]
| D
| [A]
| [C]
| (D)
| [A]
| B
|
10
| [4]
| [1]
| 4
|
|
| A
| D
| [B]
| A
| C
| C
| B
| [A]
| D
| [D]
|
4
| 6
| 6
| 7
|
|
| D
| B
| A
| D
| A
|
| A
| B
| C
| A
|
3
| 1
| [7]
| [10]
|
|
| B
| C
| D
| C
|
|
| D
| C
|
| C
|
1
| 5
| 10
| 6
|
[8]
| [3]
| 3
| 9
|
7
|
| 9
| (8)
|
[9]
|
| 2
|
|
(5)
|
(2)
| 2
|
| 2
|
|
|
|
|
| 10
| 5
| 5
|
|
| <<< These applicants were not listed.
|
Legend: (...) tentative acceptance; --- rejected
request
|
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.
|