Pairwise Rankings Explanation

Current Pairwise Rankings
Current Ratings Percentage Index

The PairWise Rankings (PWR) are a statistical tool designed to approximate the process by which the NCAA selection committee decides which 16 teams to invite to the Division I championship tournament. Although the PWR does not precisely duplicate the method used by the committee, the PWR has exactly predicted the NCAA tournament entries in each of the last eight years. (The difference in the process is that the NCAA committee doesn't actually take the final step of totaling the comparison wins, and summarizing it into a neat PWR chart. See the Selection FAQ for more details.)

Every team in the top 25 of the RPI (Rating Percentage Index) is called a "team under consideration," or TUC. The PWR method compares every TUC with every other such team, with the winner of each "comparison" earning one PWR point. After all possible comparisons are made, the points are totaled up and rankings listed accordingly.

With 25 TUCs, the greatest number of PWR points any one team could earn would be 24, by winning the comparison with each of the other 24 teams. Meanwhile, a team which lost all of its comparisons would, of course, have no PWR points.

Teams are then ranked by PWR point total, with ties broken by looking at the Rating Percentage Index (RPI). Note: this tiebreaking procedure is used solely for convenience in displaying the PWR, and will not necessarily match the committee's process. This is especially true near the end of the top 16, where the committee looks more closely at head-to-head comparisons when selecting the last few teams.

However, the committee does indeed use RPI to break ties within those head-to-head matchups. For example, if that head-to-head comparison is tied, or if there is a transitive tie in a three-way comparison (A defeats B, B defeats C, C defeats A), then RPI is indeed used to break the deadlock.

So how are teams compared? The PWR uses four criteria which are combined to make a comparison: RPI rating, record against TUCs, record against common opponents and head-to-head competition. Note that for 2006-07, TUC record only counts if both teams in the comparison have played at least 10 such games.

For an example, let's consider a hypothetical comparison between Michigan and Michigan State which might look like this:

       Michigan        vs Michigan State
RPI      0.5891  0           0.5933  1
TUC     8- 4- 1  0          8- 1- 1  1
h1H              0                   2
COP    16- 1- 1  1         12- 2- 2  0
============================================
PTS              1                   4

Michigan State has the higher RPI, and the Spartans also have the better winning percentage against other TUCs (8-1-1, .850 vs. Michigan's 8-4-1, .631). Against common opponents — teams both schools have played this season — Michigan has the edge (16-1-1, .909 vs. Michigan State's 12-2-2, .813).

Each of the above is worth one point, so Michigan State leads Michigan 2-1 in these four criteria. (Note: ties within each criteria are not broken.) Lastly, we throw in head-to-head competition, for which one comparison point is awarded for each win. Since Michigan and Michigan State have played two games this year and the Spartans have won both of them, Michigan State gets two more comparison points and the Wolverines get none.

Thus, Michigan State wins this comparison by the score of 4-1, and gets one PWR point. Notice that the final score of the comparison itself doesn't matter — Michigan State only gets one PWR point no matter what the score of the comparison itself is. If the overall comparison were tied, the team with the better RPI would receive the PWR point.