How Is RPI Calculated?
Just about every Selection Sunday when the NCAA Men's Basketball Tournament field is announced, some pundit and insider will discuss how you can't ignore one team's RPI. But what is this strange stat? In a nutshell, the Rating Percentage Index combines a team's own winning percentage with its strength of schedule. The formula is easy, but the actual RPI calculation takes some data mining.
The Basic Formula
The 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 its opponent's average winning percentage
- 25 percent of its opponent's opponent's average winning percentage
- 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 is tracking down the wins and losses of opponents and opponent's opponents records for the calculations.
The hard math comes in the adjustments. Since 2004-05, the NCAA has weighted home and road victories:
- 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. 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 their record for Team A's RPI would be considered 7-0.
NCAA 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.