Using RPI to Seed OUA Women’s Basketball Teams in the 2021-22 Season

Problem: The Ontario University Athletic (OUA) has suspended all sanctioned sports games and practices until at least January 24th, 2022. This creates an issue when the season starts again and playoff teams have played a different number of games against different opponents. How can we seed them effectively?

Solution: We can use the Rating Percentage Index (RPI), a measure of a team’s strength of schedule and winning percentage.

RPI is calculated based on the following formula:

Where, WP is the team’s winning percentage (number of games won/number of games played), OWP is the mean winning percentage of all the team’s opponents, and OOWP is the mean winning percentage of all the team’s opponents opponents.

There are some pretty relevant concerns to using RPI to seed teams (outlined here and here), but it is the way the NCAA seeded their national tournaments until 2018.

If the OUA were to end their regular season right now and seed their playoff based on RPI, this is how the rankings would look like:

I have italicized the teams that would be in the playoffs in this ranking based on the current OUA rules (top 12).

There are some pretty obvious changes to the seeding when compared to the classic solely WP% method. The biggest won is that Laurentian (3-3) would drop from the 8th seed and in the playoffs, to the 18th seed and last in the conference.

This is interesting because teams with no wins: Toronto (0-5), Algoma (0-6), and Nipissing (0-6), all rank higher than teams with at least one win. I fully agree that this makes no sense and makes RPI a tough choice, but the math is the math and I’m not going to argue with it.

The other shock is Guelph moving up 6 places to take 2nd seed in the conference. This happened because 2 of the 3 games they lost were against Brock (the #1 seeded team using both methods), and a win against McMaster.

With that, do I think the OUA should use RPI to seed their playoffs? No, I think they should use the current format but extend it and open the playoffs to all teams, allowing every team to fight for a conference championship in this broken season.