What Is RPI in College Basketball?

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The moment of truth is here. Your NCAA basketball tournament brackets stand alone, written in ink and distributed for all to see. While you try to fill the lonesome hours between games, check your knowledge of one of the key components used by many bracketologists to compare teams: the Ratings Percentage Index (RPI). 

Used since 1981, the RPI is a formula used to rank and seed college basketball teams that have never faced each other. It is based on wins, losses and the strength of their schedules.

Because not all college conferences are created equal, comparing just win percentages does not measure the relative difficulty of each team's opponents. So, the RPI factors in not only your favorite team's winning percentage (WP) but the WP of your opponents. But how do we know the teams your opponents play are any good? OK, throw in the WP of your opponents' opponents. Thankfully, the calculation stops there as research has shown that extending the formula any further doesn't help much.

For those scoring at home, here's what we have so far:

RPI = (WP * 0.25) + (OWP * 0.50) + (OOWP * 0.25) where WP is Winning Percentage, OWP is Opponents' Winning Percentage and OOWP is Opponents' Opponents' Winning Percentage

A team's basic WP is the number of wins divided by the number of wins plus losses (W / W+L). But what about those schools where the home court crazies actually have an effect on the game? Well, in 2004 the NCAA adjusted the WP calculation to lessen the effect of a home win and reward a tougher away win. A home win counts for 0.6 while a home loss costs 1.4. Similarly, an away win will earn 1.4 while an away loss costs .6.

For the OWP and the OOWP, the average of the WPs for each of the team's opponents and their opponents, respectively, are included. So, just schedule some successful Division 2 teams, right? Sorry, only games against Division 1 teams count in the calculation.

Each season beginning in January, the NCAA starts releasing the RPI ranking weekly at its official site .  Since the conference champion of each of the 30 Division 1 conferences get automatic tournament bids, there are 35 open or "at-large" teams that are chosen by a selection committee to fill out the 65 team bracket.

Of course, some have argued for expanding the tournament to even more teams:

Dan Peterson writes about sports science at his site Sports Are 80 Percent Mental.