– Schedule Strength is computed by averaging the rating of each opponent, factoring in home court advantage as appropriate. For schedule strength purposes only, unrated opponents are given a rating of the worst rated team.
– Data in the ‘LAST 5 GAMES’ column reflects a team’s performance in its last 5 games against rated teams, based on its opponents current ratings, using the same weighting principles that are used to calculate the season ratings.
What is the purpose of your ratings system?
This system is designed to be predictive. One can get a prediction by simply taking the difference in the ratings of two teams and make appropriate adjustments for home site advantage. You can probably save some work by looking at individual team pages. There you can find predictions for future games, along with the chances of winning the game outright. Check out this site to monitor the accuracy of the major systems out there.
What information goes into the ratings?
The only information I use from each game is the margin of victory/defeat and the site of the game. The result of the game (won/lost/tied) is ignored, other than it being incidental to the margin of victory/defeat. Because the system relies on only past data, it can’t anticipate personnel changes that might affect the relative strength of two teams competing in a future game.
How are the ratings calculated?
The ratings are calculated using a least squares algorithm which develops an equation based on each game. If Team A beats Team B by 15 points, then A = B+15. Of course, some adjustment is made for home site advantage where appropriate. All of the equations are then solved to minimize the mean squared error of each game. Each game is given a weight based on two factors – its significance and when it was played. The significance increases for games involving teams of similar ratings. Significance also increases for games involving teams of disparate ratings where the result is much closer than expected.
Increasing weight is also given to more recent games. In a 30 game schedule, Game 1 will weigh about 40% as much as Game 30, assuming equal significance. For about the first month of the season, some weight is given to the preseason ratings. This is done to prevent the massive amount of daily fluctuation that would otherwise occur with so little data.
Do you cap margin of victory/defeat at all?
Yes. The limit on margin of victory is based on the distribution of margin of victory for all games in a particular season. For college basketball, this works out to something around 16 points by the end of the year.
How do you handle home site advantage?
Pretty much any system out there has shown that teams play better at home. This system applies a fixed home advantage for all teams. I don’t adjust this on a daily basis during the season, instead choosing to use a home site advantage that I have calculated from previous seasons.
Any more questions? Write to firstname.lastname@example.org