NCAA Women's Basketball Ratings Percentage Index and n-Rating

The Ratings Percentage Index, or RPI, is a formula used by the NCAA to help determine which teams go to post-season tournaments and how they are seeded. The NCAA does not release an official RPI calculation during the regular season, but the basic algorithm for calculating RPIs is well publicized. This page is primarily devoted to my independent calculations of NCAA Division I women's basketball RPIs.

These are not official NCAA calculations. In fact, they are surely different than the official calculations, because the NCAA also makes several secret adjustments for the official RPI (for example, to penalize games against non-Division I opponents). However, assuming those adjustments are not too large, my RPIs should give fans a good idea where their teams stand.

I also publish n-Ratings for Division I women's basketball teams. The n-Rating is my own ranking system. It rates teams based on the margins by which they win (or lose), adjusted for home court advantage. To be precise, it rates teams according to where, on average, their margins of victory fall on a normal distribution of the year's NCAA women's basketball results. The average margins of victory are then recalculated through several iterations, taking into account the expected winning margins of opponents.

An n-Rating is intended to be an expected winning margin against an average team. It can also be used to predict the result of an upcoming game. To predict the result of a game, take the rating of the home team, add the mean home advantage, and subtract the rating of the visiting team. If the result is positive, the home team should win by that margin; if negative, the result should be the home team's margin of defeat. For games at a neutral site, just take the rating of either team and subtract the rating of the second team from it. The result is the first team's expected margin of victory (or defeat).