Often people who are not familiar with the nature and limitations of statistical methods tend to expect too much of the rating system. Ratings provide merely a comparison of performances, no more and no less. The measurement of the performance of an individual is always made relative to the performance of his competitors and both the performance of the player and of his opponents are subject to much the same random fluctuations. The measurement of the rating of an individual might well be compared with the measurement of the position of a cork bobbing up and down on the surface of agitated water with a yard stick tied to a rope and which is swaying in the wind.
In theory, there is no difference between theory and practice; In practice, there is.
The aWP is based only upon wins and losses. It basically sorts out all the chains of head-to-head-to-head wins to assign a value to the "quality" of a win based upon the quality of opponents' wins. PA-PWP is nearly the same thing, only the quality of a win is based upon the opponents' wins' quality, which is based upon their opponents ability to score and prevent scores. The ISOV is a combination of wins and Stength of Victory, which is determined by comparing every team-pair with all possible team pairs. It is the one used in the
College Football Rankings Comparison. It is also the one used to provide the predictions below.
For more information, see About the Ratings.
Actual versus Predicted MOV
Where Predicted MOV (X) and Actual MOV (Y) are both positive or both negative, the method correctly predicted the winner. When Pred is negative but Act positive, it predicted a win by the home team but the visitor won. When Pred is positive and Act negative, the visitor was predicted to win but lost. Points between the line Y=X and the X-axis represent games where the winner was picked correctly, but by an excessive margin of victory.
For the retrodictive analysis, home and visiting teams are reversed. The sign of the expected MOV matched the game results 80.7 percent of the time (503-120).