In just a few weeks time the Selection Committee for the 2015 Division I Men’s Basketball Tournament, better known as “March Madness,” will be inviting sixty-eight teams to fill a field of sixty-four. (Eight of the teams play off for four of the sixty-four seedings.) These seedings matter greatly over the three weeks of the Tournament. Top seeds win on average four out of five games they play. Teams seeded seventh win half their games, while teams seeded twelfth win about two out of every five.
Most college basketball fans know that the NCAA considers something called the “RPI,” or “Ratings Performance Index,” as a measure of each team’s strength. The Selection Committee uses RPI to help decide on at-large bids and seedings.
The RPI adjusts each team’s won-loss record by its “strength of schedule,” the won-loss record of its opponents. The NCAA also adjusts for the won-loss record of those opponents’ opponents. The team’s own performance gets only a 25% weight in the RPI. Its opponents’ record counts 50%, and their opponents records count 25%. These weightings make strength of schedule the primary determinant of RPI.
In principle these adjustments should make RPI a neutral measure of team strength and remove the effects of conference affiliations. Teams playing in “major” conferences like the ACC or Big 12 have higher RPI scores because they play a tougher schedule. In a world where seedings depended only a team’s innate abilities, it shouldn’t matter which conference that team plays in. The historical data summarized in this chart says otherwise.
The Selection Committee awards better seedings to teams playing in the major conferences than it awards to schools with identical RPI scores from weaker conferences. In the chart I’ve shown the relationship between seeding and RPI for teams grouped by their type of conference. At the top are the six “major” conferences — the ACC, Big East, Big 10, Big 12, Pac 12, and SEC. Next come the eight so-called “mid-major” conferences — Atlantic 10, Colonial Athletic, Conference USA, Horizon League, Missouri Valley, Mountain West, Western Athletic, and West Coast conferences. The Selection Committee routinely grants multiple Tournament bids to members of both these types of conferences.
The eighteen remaining conferences receive only a single Tournament invitation, the one extended to each conference’s champion. This policy forever limits teams in these conferences to also-ran status. Take a team with an RPI of 0.600. If that school plays for a team in a single-bid conference, the Committee is likely to seed that team eleventh (10.7 according to the model). Put that same team in a mid-major conference, and it would be awarded an eight seed (7.8). Playing in a major conference would earn that team a seven (7.1). Both the advantage the majors have over the mid-majors, and the advantage they both have over single-bid schools, widens with RPI.