The RPI or Ratings Percentage Index is a metric used by the NCAA Selection Committee as an aid in choosing schools for the 33 at-large spots and in seeding the post-season baseball tournament. The following is intended to illustrate how the RPI is calculated so that fans can better understand the changes in RPI values and as a result, the rankings in the RPI.
Logan Ice (OSUprof photo)
The RPI formula is an algorithm made up of three main components:
1 – Winning percentage – the season winning percentage for a team makes up 25% of the formula. But the winning percentage is adjusted by weighting the location of the games. For example, the value of a win varies with the site of the win – a road win has a value of 1.3, a neutral site win value is 1.0, and a home win value is 0.7. The reverse is true for losses – a road loss has a value of 0.7, a neutral site loss value is 1.0, and a home loss value is 1.3. The purpose of the weighting of the winning percentage is to reduce the road disadvantage faced by northern teams that must play a large part of their early season schedules on the road while southern teams play mainly at home.
While OSU’s current actual winning percentage is 0.7949 (31-8 record), the adjusted (weighted) winning percentage used in the RPI calculation is 0.7832. Since the winning percentage contributes 25% to the RPI value, then 0.7832 x 0.25 = 0.1958.
2 – Opponent’s winning percentage – makes up 50% of the formula. Sometimes a team’s RPI can drop even when winning a game over a low RPI opponent because that opponent had a poor winning percentage. Conversely, the RPI can rise even when losing to an opponent with a high winning percentage. Playing a strong schedule is important for achieving a high RPI.
3 – Opponent’s, opponents winning percentage – this makes up the final 25% of the formula. The RPI for a particular team can move up with a win over an opponent that has played other teams with high winning percentages.
Calculating the RPI
The combined opponent’s and opponent’s opponents winning percentage is sometimes referred to as the strength of schedule. For OSU at the current time, the combined opponent’s winning percentage is 0.5233. Since this component accounts for 75% of the formula, its contribution to the RPI is 0.75 x 0.5233 = 0.3925. The RPI value is then calculated as the sum of the adjusted winning percentage component and the combined opponent’s winning percentage:
RPI = 0.1958 + 0.3925 = 0.5883
Teams are ranked by RPI values, and in OSU’s current situation, the ranking of the RPI value is the 13th highest or 13th. Fans and the media often mistakenly refer to this ranking number as the RPI, but what they really mean is that OSU is ranked 13th nationally in the RPI as our RPI is really 0.5883. This indexed value and its ranking is important in comparing potential candidates for post-season play.
