It's complicated. This is a summary and no doubt an oversimplification. I have linked the primary source:
STEP 1 - THE LOCKS
There are 10 members of the selection committee. To start the process, each committee member makes two lists:
For argument's sake, let's say this phase of the process produces 17 at-large locks. 20 at-large selections to go.
STEP 2 - THE REST
The Locks are now removed from each voter's List A (as they are safely in). What's left of their List A is merged with their List B. The 10 merged lists are now compared. Any team who does not appear on at least 30% (three) lists are removed from consideration, They are OUT. Unless... they were their regular season conference champion. Every regular season conference champion is automatically under consideration, at least initially,
Let's say this process produces 50 teams competing for the remaining 20 bids.
We now enter an iterative process. Each member votes for eight remaining teams. The ten ballots are now compared and the eight teams who have the most votes are identified. Now the discussions begin. The members rank the eight teams. The top four are IN. The bottom four are returned to the pool, where they can be considered later. As before, any team that is not listed on at least three ballots is dropped from further consideration.
So at this point we have 21 at large teams (17 from Step 1, 4 from Step 2). The process repeats until all 37 at large teams are selected.
STEP 1 - THE LOCKS
There are 10 members of the selection committee. To start the process, each committee member makes two lists:
- List A - Up to 37 teams (the number of at-large bids) who should make it to the tournament, regardless of whether they may or may not qualify automatically as conference champtions.
- List B - Other teams who deserve consideration. No minimum or maximum.
For argument's sake, let's say this phase of the process produces 17 at-large locks. 20 at-large selections to go.
STEP 2 - THE REST
The Locks are now removed from each voter's List A (as they are safely in). What's left of their List A is merged with their List B. The 10 merged lists are now compared. Any team who does not appear on at least 30% (three) lists are removed from consideration, They are OUT. Unless... they were their regular season conference champion. Every regular season conference champion is automatically under consideration, at least initially,
Let's say this process produces 50 teams competing for the remaining 20 bids.
We now enter an iterative process. Each member votes for eight remaining teams. The ten ballots are now compared and the eight teams who have the most votes are identified. Now the discussions begin. The members rank the eight teams. The top four are IN. The bottom four are returned to the pool, where they can be considered later. As before, any team that is not listed on at least three ballots is dropped from further consideration.
So at this point we have 21 at large teams (17 from Step 1, 4 from Step 2). The process repeats until all 37 at large teams are selected.
