Explanation of Strength Of Schedule (SOS)


RPI Method

Strength of Schedule (SOS) is a rating which measures the difficulty of a team's schedule such that the stronger the opponents, the higher the SOS rating, or conversely, the weaker the opponents, the lower the SOS rating. In order to tabulate an SOS rating, the opponent's strength has to be evaluated. All calculations are based only on a team's W-L record and that is an indication of the opponents strength. There are two components of tbe SOS (1) the average of the the opponent's W-L percentage and (2) the average of the opponents opponent's W-L percentage. The first component is weighted 2/3 and the second component is weighted 1/3 and the sum is the SOS. For example, 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: 


                        
       Opp Rec (2/3)     Opp-Opp Rec (1/3)
          W/L PCT.           W/L PCT.
           0.667             0.333              
  
SOS = (0.667 * 0.545) + (0.333 * 0.594 = 0.562

Advantages: Uniformity throughout all NCAA Sports since it is based strictly on wins and losses. It is a straight forward and simple calculation. Disadvantages: Does not take into account goal margin of victory so that a victory by one goal carries the same weight as a victory by 15 goals. Further if there is not much crossover between two regions, than the results are meaningless when coparing teams from different regions.

The Power Rating Method

The SOS is simply the average of the opponent's power rating. If a team plays another team multiple times, then the opponent's power rating is added multiple times. We present the results of both methods for comparison in the printable link below.