RPI (ratings percentage index) is a rating that applies to a team's record and schedule such that the stronger the opponents,
the higher the RPI rating or, conversely, the weaker the opponents, the lower the RPI rating. In order to tabulate an RPI rating, the opponent's strength has to be evaluated by examining the W-L record of the opponents as well as the W-L record of the opponent's opponents.
RPI = 1/4 * team's record + 1/2 * opponent's record +
1/4 * opponent's opponent's record
Records are in the usual form of a win proportion: Wins / (Wins + Losses). Ties are treated as 1/2 win + 1/2 loss.
Here is an example of the computation:
A team has played 8 of its 12 games through the season. The team's record is 7 wins and 1 loss or 0.875.
The records for the opponents are as follows: Team A 5 3
Team B 4 3
Team C 2 5
Team D 3 4
Team E 7 1
Team F 2 5
Team G 2 5
Team H 9 0
------
34 26 (total games = 60)Therefore, the opponent's W/L record = 34 / (34 + 26) = 0.57
The records for each opponent's opponents are:
Team A 42 18
Team B 22 24
Team C 18 18
Team D 32 22
Team E 30 31
Team F 29 15
Team G 37 16
Team H 39 27
-------
249 171 (total games = 420)So, their collective W/L record = 249 / (249+171) = 0.59
The RPI for our example team is then computed as follows:
RPI = 0.25 * 0.875 + 0.50 * 0.57 + 0.25 * 0.59 = 0.654
The NCAA has not published the actual ratios they use (here 1/4, 1/2, and 1/4), so that is
currently a best guess based on the numbers used for college football.
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