How Is RPI Calculated?
Just about every Selection Sunday when the Division I NCAA Men's Basketball Tournament field is announced, some pundit and insider will discuss how the selection committee can't ignore one team's RPI ranking from the regular season.
But what is this strange college basketball metric? In a nutshell, the Rating Percentage Index combines a team's own winning percentage with the team’s strength of schedule. The formula is easy, but the actual RPI rating calculation takes some data mining.
The Basic RPI Formula
A basketball team’s RPI is calculated by using 3 factors: the team's winning percentage, the opponent's winning percentage and the winning percentage of opponents that played the opponent.
- 25 percent of the team's winning percentage
- 50 percent of the team’s opponents average winning percentage (OWP)
- 25 percent of its opponent's opponent's average winning percentage (OOWP)
Example of an RPI Calculation
Example: A team with a record of 8-0, opponents' winning percentage of .600 and opponents' opponents' winning percentage of .450 would have an RPI of 0.6625. That would read:
(1.000 x 0.25) + (0.600 x 0.50) + (0.450 x 0.25) or 0.2500 + 0.3000 + 0.1125= 0.6625.
The most difficult part of this ranking system is tracking down the wins and losses of opponents and opponent's opponents records for the calculations.
The hard math in this NCAA Evaluation tool comes in the adjustments. Since 2004-05, the NCAA has weighted home wins and road wins:
- Home victories and road losses are factored by 0.6
- Road victories and home losses are factored by 1.4
If a team is undefeated and plays an equal number of games at home and on the road, it does not affect the RPI come the postseason seeding. Games against your team are not factored into the opponent's winning percentage. In other words, if Team B is 7-1, with the only loss coming to Team A, then that team’s record for Team A's RPI would be considered 7-0 in this rating system.
Margin of victory and whether an opponent is a conference opponent or non-conference opponent are also things that are not considered when calculating this crucial metric.
NCAA Division I hockey uses a Pairwise ranking, which is a more complicated algorithm, to set its tournament field. Pairwise, however, includes the RPI as a factor, and the NCAA adjusts for any victories that would adversely lower a team's RPI.
A native of Pittsburgh, Steve Wozniak has worked as a humor writer, a sports writer, an editor and even scribbled a few ads for big-time clients back in the day. These days, he spends his time contributing to a number of websites, covering the occasional sports event, and penning the next great American novel. He studied communications and theater at University of Notre Dame.