Tuesday, July 10, 2007

Creating Power Rankings

Just as a lark, I figured I'd try devising some power rankings using my model. The basic idea behind them is this: If every team played each other once at home, once at away, who would win the most?

I tested this idea on the 2006 teams after the end of the regular season. Using my adj. rush, adj. pass, sack, adj. 3rd down conv., and turnover data, I trained a linear regression predictor on all games before 2006. Then I used the model to predict the outcomes of all 992 possible games. I created 2 separate rankings: one based on the sum of margins of victory/defeat, one based on the expected winning percentage.






































RankTeamSum of Exp. Margins
1PHI4.2027
2SD4.1368
3BAL3.8437
4JAX3.2917
5DAL2.1643
6CHI2.1514
7PIT1.9942
8NO1.8954
9IND1.7482
10NE1.5237
11MIN1.1935
12CAR1.1847
13ATL0.94039
14NYG0.84285
15MIA0.82191
16GB0.71736
17CIN0.52797
18DEN0.33802
19KC0.29031
20SF-0.685
21WAS-1.0359
22STL-1.4769
23NYJ-1.5889
24SEA-2.0378
25BUF-2.3402
26TEN-2.4492
27TB-2.8237
28ARI-3.2092
29DET-3.6094
30OAK-3.7756
31HOU-3.8764
32CLE-4.9007







































RankExp. Win %Team
1tBAL0.83871
1tPHI0.83871
3SD0.80645
4JAX0.72581
5tCHI0.66129
5tNO0.66129
7NE0.64516
8tDAL0.62903
8tCAR0.62903
10tPIT0.6129
10tIND0.6129
10tMIN0.6129
13tMIA0.59677
13tATL0.59677
15NYG0.58065
16GB0.56452
17tCIN0.54839
17tDEN0.54839
17tKC0.54839
20tSTL0.43548
20tSF0.43548
22tNYJ0.41935
22tWAS0.41935
24SEA0.33871
25TEN0.32258
26BUF0.27419
27tOAK0.19355
27tARI0.19355
29tCLE0.17742
29tHOU0.17742
29tDET0.17742
29tTB0.17742


Looking at the bottom, it's about what you'd expect. Seattle, a playoff team, shows up at #24 in both rankings, but they were 8-8 in a weak division and suffered some losses due to injury and free agency. The Jets, another playoff team, show up at #23 and #22 respectively due to weak rushing offense and defense and average passing offense and defense. Seattle and the Jets were #25 and #19 respectively in Football Outsider's 2006 DVOA rankings. Philadelphia, despite a 10-6 record, shows up at #1 with a very strong offense (14.721% VOLA rushing, 20.58% passing unadj.). Jacksonville also obtains a very high ranking (#4) despite its record, a mediocre 8-8, thanks to well above average rush offense and defense. New England is a little low compared to DVOA (#10 and #7, #5) with average and below average YPA numbers but high sack and interception rates. The Super Bowl champion Colts are at #9 and #10 (DVOA #7) with 20.142% VOLA in pass offense and 26.09% VOLA in pass defense(!too high!) but -28.29% VOLA rush defense.

So overall, the rankings turn out very similar to the DVOA rankings with individual teams gaining or losing a couple spots. There are no major disparities, however, that I can see, except maybe Dallas showing up too high in the ranking by points. It would be interesting to calculate these rankings over the season and compare these with other rankings.

Figures and article corrected on 7/12/2007 after finding errors in some box scores.

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