ryanratings: Status of Classic Ratings

Sunday, September 18, 2011

Status of Classic Ratings

The 2011 Season Beta W/L ratings have been producing mathematically significant results for the last two weeks, but the Classic ratings still aren't there yet. I'm 99%-plus certain that next week the Classic ratings will be ready to go. In case you're wondering, the only way they won't be is if East Carolina beats UAB by exactly 39 points next Saturday. Fingers crossed.

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How it works

For each team, two raw ratings are calculated; one dependent only upon wins and losses (the "W/L rating"), and the other dependent upon margin of victory (the "MOV rating"). The W/L rating for each team is simply the number of games won divided by the number of games played. The MOV rating is more complicated. I assume that a team's expected margin of victory can be modeled by a normal distribution. The distribution's mean is set equal to the average margin of victory achieved by the team over all of its games in the season. The distribution's variance is set equal to the variance of the team's margin of victory in each of its games. Based on this distribution, I calculate the probability that the team will achieve a positive margin of victory against generic opposition. This probability is the team's MOV rating.

The true "base rating" is then calculated by combining the W/L rating with the MOV rating. This combination is intended to dampen the effects of a team's running up the score, while also admitting the difference between a close game and a blowout.

Finally, the team's base rating is adjusted by the strength of its schedule. In the first round of calculations, schedule strength is set equal to the average base rating of each of the team's opponents. The team's first adjusted base rating (FABR) is then calculated by adjusting its base rating up or down depending on how strong or how weak its opposition was, as determined by this metric. In the next round, the FABRs of the team's opposition are averaged to calculate strength of schedule, and the team's base rating is again adjusted accordingly to determine the team's second adjusted base rating. I repeat this process twenty-five times so that the ratings will converge. The twenty-fifth adjusted base rating is the rating reported here.

With respect to overtime games, in calculating the MOV rating, I use the score at the end of four quarters, but in calculating the W/L rating, I treat an overtime win or loss just as I would any other win or loss.

New for 2009: Until this season, I didn't count games against non-FBS competition for any purpose. Starting in 2009, I treat games between FBS and non-FBS teams the same way as I treat games between two FBS teams, except that all non-FBS teams are aggregated for purposes of calculating schedule strength.

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Sunday, September 18, 2011

Status of Classic Ratings

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