# 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.