Explanation Of Ratings Percentage Index (RPI)

RPI (ratings percentage index) is a rating that applies to a team's record and schedule such that the stronger a team's record and the stronger a teams strength of schedule the higher the RPI. In order to tabulate an RPI rating, each opponent's strength has to be evaluated by examining its W-L record as well as the W-L record of its opponents. RPI = (1/4 * team's record) + (1/2 * opponents' record) + (1/4 * opponents' opponents' record) The second and third components are identical to the 1st and second components os the SOS. The percentages for all components are calculated by dividing wins by total games = 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   .625
   Team B        4   3   .571
   Team C        2   5   .286
   Team D        3   4   .428
   Team E        7   1   .875
   Team F        2   5   .286
   Team G        2   5   .286
   Team H        9   0  1.000
                --  --
                34  26   .545 

Note that the .545 is not based on 34/60 (.567) but on the average of each opponent's percentage in the right-hand column.
The records for each opponent's opponents are:

   Team A       42  18   .750  
   Team B       22  24   .502    
   Team C       18  18   .483
   Team D       32  22   .600
   Team E       30  31   .530
   Team F       29  15   .624
   Team G       37  16   .645
   Team H       39  27   .615
               ---  --
               249 171   .594 

Note that the .594 opponent-opponent figure above is not based on 249/(249+171) but rather is the average of the percentages in the last column. The RPI for our example team is then computed as follows:

 

 RPI = (0.25 * 0.875) + (0.50 * 0.545) + (0.25 * 0.594) = 0.600 
 

So in summary, the RPI represents a teams performance and the strength of their opponents. When employing this forumla for different sports, the weight of the first component may be increased while reducing the weights of the second and third opponents such that the sum of the weights = 1.0 In addition, sometime road wins/losses and home win/losses are weighted so that road victories are considered more difficult and home victories are less diffcult.