The PairWise Rankings (PWR) are a statistical tool designed to approximate the process by which the NCAA selection committee decides which teams get at-large bids to the 16-team NCAA tournament. Although the NCAA selection committee does not use the PWR as presented by USCHO.com, the PWR has been accurate in predicting which teams will make the tournament field.
For Division I men, all teams are included in comparisons starting in the 2013-14 season (formerly, only teams with a Ratings Percentage Index of .500 or above, or teams under consideration, were included). The PWR method compares each team with every other such team, with the winner of each “comparison” earning one PWR point. After all comparisons are made, the points are totaled up and rankings listed accordingly.
With 59 Division I men’s teams, the greatest number of PWR points any team could earn is 58, winning the comparison with every other team. Meanwhile, a team that lost all of its comparisons would have no PWR points.
Teams are then ranked by PWR point total, with ties broken by the teams’ RPI ratings, which starting in 2013-14 is weighted for home and road games and includes a quality wins bonus (QWB) for beating teams in the top 20 of the RPI (it also is weighted for home and road). See the committee’s explanation on the 2013-14 change here.
When it comes to comparing teams, the PWR uses three criteria which are combined to make a comparison: RPI, record against common opponents and head-to-head competition. Starting in 2013-14, the comparison of record against teams under consideration was dropped because all teams are now under comparison.
For an example, let’s consider a hypothetical comparison between two teams, Alpha and Bravo:
|RPI||0.5891 (0)||0.5933 (1)|
|Head-to-head wins||1 (1)||2 (2)|
|Common opponents||4-3-0, 2.250 (1)||10-3-1, 2.125 (0)|
Bravo has the higher RPI, so it earns one comparison point (shown in parentheses). Bravo has beaten Alpha twice this season, so it gets two comparison points; Alpha has beaten Bravo once this season, so it gets one comparison point.
Against common opponents — teams both schools have played this season — Bravo actually has the better overall record (a .750 winning percentage, to Alpha’s .571) but Alpha gets the edge and one comparison point because it has the better individual winning percentage against common opponents. Starting in the 2011-12 season, the common opponent calculation compares the sum of the winning percentages against each opponent, as in this example:
|vs. Charlie||2-0-0, 1.000|
|vs. Delta||1-3-0, 0.250|
|vs. Echo||1-0-0, 1.000|
|vs. Charlie||3-1-0, 0.750|
|vs. Delta||1-2-1, 0.375|
|vs. Echo||6-0-0, 1.000|
If any of the categories were tied (if, say, teams had an identical common opponents winning percentage sum), a comparison point would not be awarded for that category.
Thus, Bravo wins this comparison by the score of 3-2, and gets one PWR point. Notice that the final score of the comparison itself doesn’t matter — Bravo gets only 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.