CHSAA has moved to a new RPI system for postseason all team sports.
Below are answers to common questions surrounding the RPI system.
What's the RPI formula? And where did it come from?
RPI stands for Ratings Percentage Index. This Wikipedia page is a good starting point for those looking to become familiar with the formula. In short, it is a way to measure a team's strength relative to other teams, based largely on the strength of their schedules.
CHSAA first became interested in using an RPI system when searching for a way to standardize all postseason qualification processes. It was also used by the football committee in 2015 as a component to the seeding criteria, following a presentation and suggestion from community members. The RPI formula is used by both the NCAA and NAIA, among other organizations, as part of their postseason system. In August 2015, CHSAA's board of directors mandated that all committees use RPI for postseason qualification.
What percentages are being used in the formula?
The standard RPI formula is:
RPI = (¼ × WP) + (½ × OWP) + (¼ × OOWP)
That formula is currently being used by all team sports during the 2016-17 school year, with one exception.
Baseball is using the following formula for the spring 2017 season:
RPI = (0.35 × WP) + (0.35 × OWP) + (0.30 × OOWP)
Why use RPI instead of another type of rating system?
A major advantage to the RPI is the transparency that comes along with its accuracy. The components of the formula are known, and its results can be easily replicated.
What data will be used in the RPI formula?
All games played in the regular season shall be counted toward the RPI calculation, with the exception of games against non-varsity opponents.
Where will be the RPI standings be published?
The official CHSAA RPI standings will be published on CHSAANow.com, specifically here. It is worth noting that any RPI data published elsewhere is unofficial and should be viewed with skepticism as it may not be correct.
How are the components of the formula specifically calculated?
- Winning percentage (WP): Divide the number of wins by the number of total games played. A tie is worth half a win. If a win in an individual contest gives that contest a winning percentage of 1.00, a tie would give that individual contest a winning percentage of .500 for both teams.
- Opponents' winning percentage (OWP): Average the winning percentages of a team's opponents. (Note: This is not calculated via the combined record of the opponents, instead by averaging each winning percentage of the opponents.) All games involving the team whose RPI is being calculated are ignored in this process.
- Opponents' opponents winning percentage (OOWP): The same process as described above, except calculated for the opponents of a team's opponents. Note that there is an exception for out-of-state teams, which is addressed below.
How will out-of-state opponents be handled?
When calculating out-of-state opponents, their direct winning percentage (for example, .750) will count toward the formula, but each of their opponents will have a .500 winning percentage assigned. Were this not the case, schools would be chasing tens of thousands of opponents of out-of-state opponents over the course of a season, and there is no way to ensure the accuracy of that data.
The .500 figure was selected because it is the average value of opponents' opponents winning percentages across all sports in the data we've run.
Are games against non-varsity teams counted toward the RPI calculation?
No, they are not.
How will cross-classification games be handled?
There are two answers to this question. One pertains to football, and the other pertains to the rest of the sports.
Football will use a modifier to handle these cross-classification games. Other sports will not. The reason for the difference is football plays a 10-game regular season, which is far-and-away the fewest of any sport. (By comparison, for example, baseball plays a 19-game regular season, and basketball plays 23.) Thus, there is less data to work with in football to ensure the accuracy of the result. Using a modifier helps to increase the accuracy.
The modifier for football will be a 15 percent difference. This number was arrived at when comparing the average RPI of football teams in different classifications over the past couple of years. On average, there was a 15 percent difference from a 5A team to a 4A team, from a 4A team to a 3A team, and so on.
As was the case with the Wild Card point system which the RPI will replace in football, there will be a one-time exception for a team playing down. That is to say, when a 3A team plays a 2A opponent for the first time on their schedule, that 2A opponent will count as a 3A team. Subsequent games against teams from lower classifications will count as their true classification.
Unlike the Wild Card point system, however, this modifier only comes into play when a team wins. Under the modified RPI system which will be used in football, each game is assigned a value based on that team's classification. Again, there is a 15 percent difference between them. Those (rounded) values are:
So, for example, a 3A team will always have a game value of 1.749, regardless of who they're playing. The value of the win changes according to their opponent (unless the exemption comes into play). The result gives us a modified winning percentage. This is the number that will be used throughout the formula, including for their opponents, and the opponents of their opponents.
Using our example, let's pretend that 3A team (call them Team A) plays another 3A team (Team B), and beats them. They then play a different 3A team (Team C) and lose to them. The third week, the play a 2A team (Team D), and beat them. Finally, they play yet another 2A team (Team E), and beat them as well. Here's what the calculation would for Team A look like:
|Opponent||Result||Game Value||Win Value||Winning Percentage|
Now, Team A in this scenario is 3-1. Their true (unmodified) winning percentage would be 0.75. However, with this modified system, where their total win value (roughly 5.019) is divided by their total game value (6.996), their modified winning percentage is 0.717.
Over the course of a season, if Team A were to go 9-1 with wins over all 3A teams the rest of the way, their modified winning percentage would be 0.887 (as opposed to a true winning percentage of 0.900). It is worth remembering that this number is 25 percent of the overall formula.
Again, all other sports will not be using the modified system because their regular seasons are much longer.
What happens if two teams are tied in the final RPI standings?
We have created a tiebreaker for this unlikely scenario. It is as follows:
- Head-to-head result between the two teams
- Winning percentage
- Opponents' winning percentage
- Opponents' opponents winning percentage
- Highest-rated win (according to the final RPI standings)
- Next-highest rated win (exhaust all possibilities)
- Coin flip
The only reason for the coin flip is as a last result if all other scenarios happen to be tied.
How should teams be scheduling?
The main thing to remember with the RPI is it takes an entire schedule into account. Do not fret over scheduling one game. Instead, see the entire schedule as a whole and try to judge if it will be tough or not.
Does the score of the contest matter in the RPI formula?
Only in that it gives a winner and a loser (or results in a tie). There is no factor for score differential in the RPI formula. A 1-0 win counts the same as 100-1.
What happens if a game is cancelled and can't be rescheduled?
Because the RPI system works off of averages, it won't make a difference in the final formula if a game cannot be rescheduled. It would not penalize, nor benefit, any team involved in that scenario.
Where should we be reporting scores?
Continue reporting scores to MaxPreps. The official RPI feed will be calculated off of results entered into that platform.
How often will the RPI standings be published?
The RPI standings will not publish for the first time until a season hits the midway point.
Once they do, feeds are updated nightly during the regular season.
Note that not all sports have a feed. Sports without feeds will have their standings updated manually each week.