INTRODUCTION
The NCAA RPI formula assigns values to:
1. A Team's Winning Percentage (WP); and
2. A Team's Strength of Schedule (SoS).
The formula is set so that each of these values accounts for 50%, in effective weight, of the Team's NCAA RPI rating. The NCAA publicly acknowledges these effective weights.
The NCAA SoS value consists of two elements:
1. The average of a Team's Opponents' Winning Percntages (OWP); and
2. The average of a Team's Opponents' Opponents' Winning Percentages (OOWP).
The formula is set so that OWP accounts for 80% and OOWP for 20% of SoS, in effective weights. The NCAA does not publicly acknowledge these effective weights.
Thus overall, the NCAA RPI value for a team consists of, in effective weights:
Winning Percentage 50%
Average of Opponents' Winning Percentages 40%
Average of Opponents' Opponents' Winning Percentages 10%
This compares to the NCAA RPI SoS contributor value for a team which consists of, in effective weights:
Winning Percentage 80%
Opponents' Winning Percentage 20%
Because of the differences in these calculation methods, a team's NCAA RPI rating and rank can be and often are very different than its NCAA RPI SoS Contributor value and rank. The NCAA does not publish teams' SoS Contributor values and ranks and does not discuss that they are different than teams' NCAA RPI ratings and ranks.
How different are these two sets of numbers? For the formula the NCAA currently uses:
The average difference between a team's NCAA RPI rank and its NCAA RPI SoS Contributor rank is 31.3 positions.
The median difference is 24 positions.
The maximum difference, since 2010, is 177 positions.
EFFECT OF THE NCAA RPI v SoS VALUE DIFFERENCES ON CONFERENCES
In the Team Histories and Simulated 2025 Balanced RPI Ranks workbook, I have calculated for each team, for each year since 2010, the difference between the average NCAA RPI rank of its conference opponents and the average NCAA RPI SoS Contributor rank of those same opponents. I then have calculated the average of those numbers over the period from 2010 through 2024. I have done the same for non-conference opponents.
To show the effect of the NCAA RPI v SoS Value differences on conferences, I will start with the ACC as an example. Here is a chart for Clemson, for whom the effect is typical for an ACC team. Scroll to the right, if necessary, to see the entire chart:
In the chart, the blue lines are for Clemson's ACC conference opponents. The dark blue line shows its conference opponents' average NCAA RPI ranks, year by year. The light blue line shows their average NCAA formula ranks as SoS contributors. As the chart shows, Clemson's ACC opponents' ranks as SoS contributors are consistently and significantly poorer than their actual NCAA RPI ranks, to the tune of 39 positions poorer on average.
The red and orange lines are for Clemson's non-conference opponents. There is more variability here since Clemson's non-conference schedule can change significantly from year to year. Nevertheless, in general Clemson's non-conference opponents' ranks as SoS contributors are poorer than their actual NCAA RPI ranks, to the tune of 16 positions on average.
The net effect on Clemson is that the NCAA RPI formula seriously underrates its conference opponents and also underrates its non-conference opponents. This causes the formula as a whole to underrate Clemson.
Here is what the numbers show for the Atlantic Coast Conference as a whole. (SMU, at the bottom of the table, is new to the conference and from a significantly weaker conferece and thus is not representative of the ACC's teams. Stanford and California, at the top, are new but from the relatively equivalent Pac 12 and are relatively representative for the ACC.)
If you look at the third column of numbers for the teams, you will get a clear picture of how the NCAA RPI treats the ACC teams for SoS Contributor purposes. Each team's average conference opponents' SoS Contribution to the team's NCAA RPI is 35 to 45 positions poorer than it should be according to the full NCAA RPI. In addition, all of the teams' non-conference opponents' SoS Contributions are poorer than they should be, though to a lesser and more varying degree.
Next, I will show the information for a conference in the middle where the differences between teams' conference opponents' NCAA RPI ranks and NCAA formula ranks as SoS contributors are similar. The Atlantic 10 is a good example, with Richmond as a representative team:
As you can see, for Richmond, its conference opponents' NCAA RPI ranks and their NCAA formula RPI SoS contributor ranks are quite similar. On average, its conference opponents' NCAA formula SoS contributor ranks are only 2 positions poorer than their NCAA RPI ranks. Although for Richmond's non-conference opponents there is more variability from year to year, overall on average there is no difference between the opponents' NCAA formula SoS contributor ranks and the NCAA RPI ranks.
Here is the table for the Atlantic 10 as a whole:
As you can see, for the Atlantic 10, the NCAA RPI formula gets their ratings about right. (Note: Loyola Chicago joined the Atlantic 10 in 2022 and its numbers are not representative for the Atlantic 10.)
However, since the RPI significantly underrates teams from conferences at the level of the ACC, the NCAA RPI cannot get the Atlantic 10 rankings right, since teams from conferences at the level of the ACC might pass them in the rankings if properly rated.
And, here is information for a conference at the bottom of the spectrum, where teams' conference opponents' NCAA formula SoS contributor ranks are significantly better than their NCAA RPI ranks. The Southland is the example, with Northwestern State as a representative team:
You can see that Northwestern State's conference opponents' NCAA formula SoS contributor ranks are better than their NCAA RPI ranks, on average 25 positions better. Likewise its non-conference opponents' NCAA formula SoS contributor ranks are better, although less so, on average 13 positions better.
Here is the table for the Southland as a whole:
As you can see, the NCAA formula consistently over-ranks the Southland teams as NCAA formula SoS contributors and thus consistently overrates its teams. For a conference like this, where it matters from an NCAA Tournament perspective, is if a team from the conference has an unusually good year and achieves an NCAA RPI rank that puts it in consideration for an NCAA Tournament at large selection or even for a seed. In that case, the team will be over-ranked and thus may have bumped out of consideration a team from a strong conference, especially since teams from strong conferences are underrated.
Below is a table of all the teams, arranged by conference so you can see the full NCAA RPI to NCAA RPI SoS rankings contrast for each conference. It provides as clear and stark a demonstration as possible of the NCAA RPI's problem rating teams from a conference in relation to teams from other conferences. The way the NCAA RPI is constructed, as discussed above in the Introduction, it can't do this properly.
When is this a problem from an NCAA Tournament perspective? It is a problem whenever teams from under-ranked and over-ranked conferences are in the same NCAA RPI rank area for seeding or for at large selections. And, it is a problem when teams from under-ranked conferences are outside the historic range for consideration for at large selections but really should be inside the range; and when teams from over-ranked conferences are inside the historic range for consideration for at large selections but should be outside the range. Does the NCAA give the Women's Soccer Committee information about the NCAA RPI rank versus NCAA formula SoS Contributor rank differences so that the Committee can adjust its evaulations of teams to take the differences into account? No. Even if the NCAA were to give the Committee that information, would Committee members have the sophistication to properly take the differences into account? Unlikely. The solution? Stop using the NCAA RPI and replace it with a better system.
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