How It Works
The Pairwise ranking is comprised of three different elements: Head-to-head results, results from common opponents, and RPI.
Head-to-Head:
A school is given one point per head-to-head win over an opponent. For example, in 2014, Arizona defeated Oregon once, and Oregon later defeated Arizona once. Therefore, each team receives one point. Each head to head win counts as a comparison point in the final total.
Common Opponents:
The common opponent metric takes the sum of the winning percentage for schools that both teams have played during the season. In 2014, Arizona and Oregon shared six teams on their schedule. Oregon went 6-0, while Arizona went 5-1. Oregon, therefore, had a 6.000 total for their six winning percentages of 1.000. Arizona earned 5.000 for five winning percentages of 1.000 and a winning percentage of 0.000 against UCLA. Unlike the head-to-head comparison, Oregon only earns one comparison point here.
RPI:
The Ratings Percentage Index (RPI) is used across many sports. There are three components to this metric: Winning Percentage, Opponents' Winning Percentage, and Opponents' Opponents’ Winning Percentage.
Winning Percentage (WP): Generally, this is not the face value winning percentage of a team’s record. Many sports have adjusted this to account for perceived home field advantage. In NCAA basketball, where the home team wins approximately two-thirds of the time, a home win counts as .6 while an away win is 1.4. The weights are reversed for losses. Neutral games still count as 1 and 1. Hockey uses 0.8 and 1.2. College football has similar home field winning percentages as college basketball, so the College Football Pairwise also weighs wins and losses using 0.6 and 1.4.
Opponent’s Winning Percentage (OWP): The average winning percentage of a team’s opponents, not counting games involving the team being measured. The unweighted winning percentage is used in these calculations.
Opponent’s Opponents’ Winning Percentage (OOWP): The average winning percentage of the opponents of a team’s opponent. This component does take into account the team being measured.
Finally, the metrics are each weighted to bring them together. College hockey currently uses 25-21-54 to represent WP-OWP-OOWP, and in the past has made winning percentage as much as 35%. Basketball uses 25-50-25.
Due to the nature of college football’s limited schedule, there is less margin for error when it comes to losing in the regular season. In the CFBPW, the Winning Percentage metric is weighted as thirty percent of a team’s RPI score. The remaining seventy percent of the equation is then split into thirds. One third is allocated to OWP and the remaining two thirds are given to OOPW. The result is a final approximate ratio of 30-23-47.
To finalize the Oregon-Arizona example, here is the final comparison:
Arizona Oregon
Head to head: 1-1 (1) 1-1 (1)
Common Opponent: 5-1, 5.000 (0) 6-0, 6.000 (1)
RPI: .6159 (0) .6550 (1)
Total Points: 1 3
Oregon wins the comparison versus Arizona and earns one PWC point. In the event of a tie, the school with the higher RPI will be awarded the PWC point.
This process is used to compare every team against one another. A team cannot win a comparison with itself, so the highest PWC score possible is 130 (130 FBS teams plus FCS dummy team). Teams are ranked based upon their PWC score, with RPI being used as a tiebreaker.