so much for that
John Whelan
Bradley-Terry Statistical Rating (KRACH) for FBS Football
What do the numbers say?
The Bradley-Terry method applied to college football.
A couple of notes regarding the calculations. I use the Bradley-Terry method for determining the ratings. This is an iterative, statistical rating that computes a hypothetical round-robin winning percentage if all teams played each other. Clearly, that's not the case in college football, and this method gives infinite results if teams are undefeated. This problem is 'solved' for the sake of comparison by adding a fictitious tie to each team's record.
Further notes:
- Game results are pulled from the NCAAFootball.com.
- Blogpoll results are pulled from SBNation.
- There are a lot of explanatory notes and links; I put those at the end of the post so people who don't care about them can skip them and get right to the results. There is also a link to all my results.
- For brevity, I only listed the top 20 here. For those who are interested, I also listed Michigan's position, FYI.
- I release this after all the major polls come out to avoid 'influencing' anybody's vote.
To the numbers...
| Through games of 2010.11.06 | |||||
| Team | Rating | Previous | Delta | Blogpoll | |
| 1 | Auburn | 85.581 | 1 | 0 | 2 |
| 2 | Oregon | 38.314 | 4 | 2 | 1 |
| 3 | T-C-U | 37.076 | 3 | 0 | 3 |
| 4 | Boise State | 28.029 | 2 | -2 | 4 |
| 5 | L-S-U | 27.484 | 5 | 0 | 5 |
| 6 | Stanford | 15.449 | 13 | 7 | 6 |
| 7 | Oklahoma State | 15.175 | 12 | 5 | 10 |
| 8 | Nebraska | 14.947 | 8 | 0 | 8 |
| 9 | Michigan State | 12.443 | 9 | 0 | 11 |
| 10 | Wisconsin | 12.340 | 11 | 1 | 7 |
| 11 | Utah | 9.372 | 7 | -4 | 15 |
| 12 | Virginia Tech | 8.671 | 14 | 2 | 20 |
| 13 | Iowa | 8.383 | 17 | 4 | 13 |
| 14 | Alabama | 8.000 | 16 | 2 | 12 |
| 15 | Arkansas | 7.989 | 20 | 5 | 14 |
| 16 | Miss State | 7.656 | 19 | 3 | 18 |
| 17 | Ohio State | 7.608 | 18 | 1 | 9 |
| 18 | Missouri | 7.282 | 6 | -12 | 17 |
| 19 | Arizona | 6.162 | 15 | -4 | 16 |
| 20 | Oklahoma | 5.663 | 10 | -10 | 19 |
| -- | -- | -- | -- | -- | -- |
| 29 | Michigan | 2.621 | 41 | 12 | NR |
Auburn is pulling away as the number one team. Oregon has finally caught up with everybody's ranking due to strength of schedule, and Boise St. has begun to fall for the same reason. The bonus for being undefeated this far into the season is starting to balance out with perceived strength of schedule, as LSU is nipping at the Broncos heels.
As a point of comparison, it lines up really well with the blogpoll. Two outliers: blogpollers really like Ohio State, and they really dislike Virginia Tech (see discussion of limitations, below).
There's a pretty significant drop-off from #5 LSU to #6 Stanford, and another notable drop-off from #10 Wisconsin to #11 Utah. I think this supports the notion that a 16-team tournament would be sufficient to include all the top teams. If you're in the muddle around 16, there really isn't all that much to complain about if you're left out.
The conference breakdown in the top 10 and top 16 (non-BCS conferences in parentheses):
| Conference | Top 10 | Top 16 |
| SEC: | 2 | 5 |
| Big Ten: | 2 | 3 |
| Big 12: | 2 | 2 |
| Pac 10: | 2 | 2 |
| (MWC): | 1 | 2 |
| ACC: | 0 | 1 |
| (WAC): | 1 | 1 |
| Big East: | 0 | 0 |
| (Conference USA): | 0 | 0 |
| (Independent): | 0 | 0 |
| (MAC): | 0 | 0 |
| (Sun Belt): | 0 | 0 |
The top 10 has roughly equal representation from the BCS conferences. Looking at the top 16, a bias toward the SEC begins to emerge, with 5 teams, including those in spots 14-16. Not surprisingly, the Big East is absent, and the ACC is, well, underrepresented. TCU, Boise St. and Utah are ranked above all comers from these conferences, including Virginia Tech, who lost to Boise St. and, as we all know, James Madison. The nagging question remains: how do you compare the relative strengths of conferences when they don't play each other?
The next few weeks should be interesting.
Technical notes
I explained the mathematics of the calculations in much more detail last year. Wikipedia has a nice explanation of the foundation of the Bradley-Terry method.
Discussion of limitations
Many of the strengths of this method are addressed at U.S. College Hockey Online.
That said, there's always a bit of resistance when I post this rating. It's one additional data point. It's not even my opinion, and it doesn't mean your team is better or worse than you think it is. It attempts to look objectively at how teams would fare, should they play every other team. There are some limitations, namely the infinite results, and incomparability, of undefeated teams. As with any statistical calculation, sample size is important; while there are only ~12 games per team, there are ~120 teams. One could argue the merits of using any sort of statistical calculation on said sample. Also, it should be pointed out that games against FCS teams are ignored. This is a double-edged sword: teams don't get credit for beating up on FCS teams, but Virginia Tech effectively gets a pass for losing to James Madison.
Brian pointed out another interesting anomaly (it's the double star at the very bottom) in last year's end-of-season college hockey KRACH. A similar effect can be seen in this rating, as discussed above. So, why does this happen? Like college football, there's little overlap between conferences, teams tend to get compartmentalised.
As with any tool, it's only as good as its user; we can't blindly take the results as fact. One possible solution is to take the top 30 teams at the end of the season and run a KRACH on only those teams. Although, for any hypothetical tournament, I would strongly support the inclusion of all conference champions.
What if I want to see the entire rating, and results for each week?
All the results are available, if you'd like to see the numbers yourself. As I said last year, John Whelan freely gave me the perl script in 1998 to calculate KRACH for ACHA club hockey teams, so I'm happy to share the script and input data if you don't want to write it yourself. And I am fallible. There's a lot of data to crunch, and I copied and pasted from the NCAA site; there may be errors. If you find one, please bring it to my attention and I'll make the fix posthaste.
Modified Terry-Bradley Statistical Ranking for Week Ending 2009.11.29
- Texas overtakes TCU
- Oregon and Georgia Tech swap
- LSU jumps 7 spots after a similar fall last week.
- USC jumps 7 spots after beating UCLA
- BYU is up 10 spots after knocking off Utah
- Pittsburgh drops 10 spots after losing to West Virginia
Interestingly, I don't think there's any way Florida or Alabama falls further than 4th; and they end up with the top 2 SOS rankings by a significant margin (the SEC takes 6 of the top 7 spots here). EDIT: If all the underdogs win this week, Alabama and Florida end up 1 and 2, respectively.
This week's top 20:
| Team | Pvs | +/- | Rank | KRACH | RRWP | Record Rank | W | L | T | Win % | SOS Rank | SOS |
| Alabama | 1 | 0 | 1 | 63.764 | 0.960 | 1 | 11 | 0 | 0 | 1.000 | 6 | 2.772 |
| Florida | 2 | 0 | 2 | 54.767 | 0.955 | 1 | 11 | 0 | 0 | 1.000 | 11 | 2.381 |
| Cincinnati | 3 | 0 | 3 | 36.668 | 0.937 | 1 | 10 | 0 | 0 | 1.000 | 32 | 1.746 |
| Texas | 5 | 1 | 4 | 31.291 | 0.929 | 1 | 12 | 0 | 0 | 1.000 | 52 | 1.252 |
| TCU | 4 | -1 | 5 | 29.027 | 0.925 | 1 | 11 | 0 | 0 | 1.000 | 50 | 1.262 |
| Boise State | 6 | 0 | 6 | 27.779 | 0.922 | 1 | 11 | 0 | 0 | 1.000 | 53 | 1.208 |
| Oregon | 8 | 1 | 7 | 11.106 | 0.851 | 3 | 9 | 2 | 0 | 0.818 | 4 | 2.923 |
| Georgia Tech | 7 | -1 | 8 | 7.822 | 0.814 | 3 | 9 | 2 | 0 | 0.818 | 19 | 2.058 |
| LSU | 16 | 7 | 9 | 7.745 | 0.813 | 5 | 9 | 3 | 0 | 0.750 | 5 | 2.853 |
| Ohio State | 10 | 0 | 10 | 6.409 | 0.791 | 2 | 10 | 2 | 0 | 0.833 | 37 | 1.526 |
| Virginia Tech | 11 | 0 | 11 | 6.347 | 0.790 | 5 | 9 | 3 | 0 | 0.750 | 12 | 2.339 |
| Iowa | 12 | 0 | 12 | 6.256 | 0.788 | 3 | 9 | 2 | 0 | 0.818 | 33 | 1.646 |
| USC | 20 | 7 | 13 | 5.493 | 0.771 | 6 | 8 | 3 | 0 | 0.727 | 14 | 2.262 |
| Miami (FL) | 15 | 1 | 14 | 5.280 | 0.766 | 6 | 8 | 3 | 0 | 0.727 | 16 | 2.174 |
| Oregon State | 19 | 4 | 15 | 5.262 | 0.765 | 7 | 7 | 3 | 0 | 0.700 | 9 | 2.456 |
| Penn State | 13 | -3 | 16 | 5.011 | 0.759 | 3 | 9 | 2 | 0 | 0.818 | 46 | 1.319 |
| Brigham Young | 27 | 10 | 17 | 4.956 | 0.757 | 2 | 10 | 2 | 0 | 0.833 | 55 | 1.180 |
| California | 21 | 3 | 18 | 4.769 | 0.752 | 7 | 7 | 3 | 0 | 0.700 | 15 | 2.226 |
| Pittsburgh | 9 | -10 | 19 | 4.674 | 0.749 | 4 | 8 | 2 | 0 | 0.800 | 44 | 1.375 |
| Oklahoma State | 14 | -6 | 20 | 4.301 | 0.738 | 6 | 8 | 3 | 0 | 0.727 | 30 | 1.771 |
Modified Terry-Bradley Statistical Ranking for Week Ending 2009.11.22
Apologies for the tardiness of this post - I meant to post this when the blogpoll came out, but I missed that, then it was the weekend. And there's not much change at the top.
I'll post this week's results after the blogpoll comes out.
Here's the top 20 from last week (through games of 2009.11.22):
| Team | Pvs | +/- | Rank | KRACH | RRWP | Record Rank | W | L | T | Win % | SOS Rank | SOS |
| Alabama | 1 | 0 | 1 | 50.726 | 0.952 | 1 | 10 | 0 | 0 | 1.000 | 8 | 2.416 |
| Florida | 2 | 0 | 2 | 38.709 | 0.940 | 1 | 10 | 0 | 0 | 1.000 | 24 | 1.843 |
| Cincinnati | 3 | 0 | 3 | 35.500 | 0.936 | 1 | 9 | 0 | 0 | 1.000 | 22 | 1.868 |
| TCU | 4 | 0 | 4 | 30.850 | 0.928 | 1 | 10 | 0 | 0 | 1.000 | 42 | 1.469 |
| Texas | 5 | 0 | 5 | 29.226 | 0.925 | 1 | 11 | 0 | 0 | 1.000 | 53 | 1.271 |
| Boise State | 6 | 0 | 6 | 22.462 | 0.908 | 1 | 10 | 0 | 0 | 1.000 | 59 | 1.070 |
| Georgia Tech | 7 | 0 | 7 | 15.023 | 0.878 | 2 | 9 | 1 | 0 | 0.900 | 9 | 2.372 |
| Oregon | 9 | 1 | 8 | 10.346 | 0.843 | 5 | 9 | 2 | 0 | 0.818 | 2 | 2.723 |
| Pittsburgh | 10 | 1 | 9 | 8.102 | 0.817 | 3 | 8 | 1 | 0 | 0.889 | 44 | 1.430 |
| Ohio State | 11 | 1 | 10 | 7.223 | 0.804 | 4 | 10 | 2 | 0 | 0.833 | 29 | 1.720 |
| Virginia Tech | 13 | 2 | 11 | 7.074 | 0.801 | 7 | 8 | 3 | 0 | 0.727 | 1 | 2.913 |
| Iowa | 12 | 0 | 12 | 6.729 | 0.795 | 5 | 9 | 2 | 0 | 0.818 | 26 | 1.771 |
| Penn State | 15 | 2 | 13 | 6.109 | 0.783 | 5 | 9 | 2 | 0 | 0.818 | 35 | 1.608 |
| Oklahoma State | 14 | 0 | 14 | 5.917 | 0.779 | 6 | 8 | 2 | 0 | 0.800 | 28 | 1.740 |
| Miami (FL) | 19 | 4 | 15 | 5.415 | 0.768 | 8 | 7 | 3 | 0 | 0.700 | 5 | 2.527 |
| LSU | 8 | -8 | 16 | 5.158 | 0.761 | 7 | 8 | 3 | 0 | 0.727 | 17 | 2.124 |
| Clemson | 20 | 3 | 17 | 4.903 | 0.755 | 8 | 7 | 3 | 0 | 0.700 | 10 | 2.288 |
| North Carolina | 26 | 8 | 18 | 4.783 | 0.751 | 9 | 6 | 3 | 0 | 0.667 | 3 | 2.575 |
| Oregon State | 16 | -3 | 19 | 4.723 | 0.750 | 8 | 7 | 3 | 0 | 0.700 | 13 | 2.204 |
| USC | 17 | -3 | 20 | 4.585 | 0.745 | 8 | 7 | 3 | 0 | 0.700 | 16 | 2.139 |
KRACH 19 Nov 2009 - Addresses most of the problems from last week
I put a bit of effort in cleaning up my code to address some of the problems from last week:
- Undefeated and winless teams: I added the fictitious tie. Now there's a path from every team to every other team. While this is a hack, it's reasonable and about as far as I really care to go with it. I also calculated the round-robin winning percentage (RRWP) and KRACH strength of schedule (SOS). These are useful metrics for comparing teams that don't line up very well, as per John Whelan's KRACH site. Now the undefeated and winless teams can be compared with multiple data elements.
- Rasmus: Open source: The original Pairwise and KRACH code was freely given to me years ago by John Whelan. This code is my own, based only on the information given in his KRACH site; given that, I'm comfortable sharing my code, so long as the user gives due credit to John and Ken Butler.
- joeyb: Undefeated teams will always rate better than teams with losses: To investigate this, I created a fictitious team that was 10-0 with wins against only the bottom ten teams. It rated out at #37, well below several 1- and 2-loss teams.
- SpartanDan: Top teams are ranked backwards: You are correct, sir. I mistakenly assumed that a larger deviation from predicted meant a less accurate KRACH. This has been fixed, as in 1) above, with the RRWP, SOS and fictitious tie.
- Seth9: The rating doesn't apply to college football: You may be right on this. It's still curious, and now trivial, for me to crunch the numbers. EDIT: But is this any less applicable than any of the computer ratings used in the BCS? And it certainly does not have the bias and politicking associated with opinion polls.
Again, this rating includes all D-IA games through 15 November 2009:
| Team | BlogPoll | BCS | Rank | KRACH | RRWP | Record Rank | W | L | T | Win % | SOS Rank | SOS |
| Alabama | 1 | 2 | 1 | 50.413 | 0.953 | 1 | 10 | 0 | 0 | 1.000 | 10 | 2.401 |
| Florida | 3 | 1 | 2 | 43.477 | 0.946 | 1 | 9 | 0 | 0 | 1.000 | 15 | 2.288 |
| Cincinnati | 5 | 5 | 3 | 36.050 | 0.937 | 1 | 9 | 0 | 0 | 1.000 | 23 | 1.897 |
| TCU | 4 | 4 | 4 | 29.380 | 0.926 | 1 | 9 | 0 | 0 | 1.000 | 35 | 1.546 |
| Texas | 2 | 3 | 5 | 26.406 | 0.920 | 1 | 10 | 0 | 0 | 1.000 | 52 | 1.257 |
| Boise State | 6 | 6 | 6 | 21.243 | 0.906 | 1 | 9 | 0 | 0 | 1.000 | 59 | 1.118 |
| Georgia Tech | 7 | 7 | 7 | 13.464 | 0.870 | 2 | 9 | 1 | 0 | 0.900 | 18 | 2.126 |
| LSU | 11 | 8 | 8 | 9.599 | 0.837 | 5 | 8 | 2 | 0 | 0.800 | 2 | 2.823 |
| Oregon | 9 | 11 | 9 | 9.141 | 0.832 | 5 | 8 | 2 | 0 | 0.800 | 3 | 2.688 |
| Pittsburgh | 8 | 9 | 10 | 8.655 | 0.826 | 3 | 8 | 1 | 0 | 0.889 | 37 | 1.527 |
| Ohio State | 10 | 10 | 11 | 7.289 | 0.807 | 4 | 9 | 2 | 0 | 0.818 | 22 | 1.918 |
| Iowa | 14 | 13 | 12 | 6.292 | 0.789 | 5 | 8 | 2 | 0 | 0.800 | 24 | 1.851 |
| Virginia Tech | 16 | 15 | 13 | 6.103 | 0.785 | 8 | 7 | 3 | 0 | 0.700 | 1 | 2.848 |
| Oklahoma State | 12 | 12 | 14 | 5.436 | 0.770 | 6 | 7 | 2 | 0 | 0.778 | 26 | 1.812 |
| Penn State | 15 | 14 | 15 | 5.061 | 0.761 | 5 | 8 | 2 | 0 | 0.800 | 40 | 1.489 |
| Oregon State | 19 | 19 | 16 | 4.967 | 0.758 | 9 | 6 | 3 | 0 | 0.667 | 4 | 2.675 |
| USC | 21 | 18 | 17 | 4.954 | 0.758 | 8 | 7 | 3 | 0 | 0.700 | 14 | 2.312 |
| Wisconsin | 17 | 16 | 18 | 4.574 | 0.747 | 6 | 7 | 2 | 0 | 0.778 | 38 | 1.525 |
| Miami (FL) | 20 | 20 | 19 | 4.544 | 0.746 | 9 | 6 | 3 | 0 | 0.667 | 8 | 2.447 |
| Clemson | 18 | 23 | 20 | 4.393 | 0.741 | 9 | 6 | 3 | 0 | 0.667 | 12 | 2.365 |
| Rutgers | 21 | 4.372 | 0.741 | 7 | 5 | 2 | 0 | 0.714 | 20 | 1.987 | ||
| Utah | 23 | 21 | 22 | 3.965 | 0.727 | 5 | 8 | 2 | 0 | 0.800 | 56 | 1.166 |
| Stanford | 13 | 17 | 23 | 3.825 | 0.721 | 8 | 7 | 3 | 0 | 0.700 | 27 | 1.785 |
| California | 25 | 24 | 3.679 | 0.716 | 9 | 6 | 3 | 0 | 0.667 | 21 | 1.981 | |
| Temple | 25 | 3.607 | 0.713 | 3 | 8 | 1 | 0 | 0.889 | 88 | 0.636 | ||
| North Carolina | 25 | 26 | 3.504 | 0.708 | 11 | 5 | 3 | 0 | 0.625 | 16 | 2.230 | |
| Arizona | 27 | 3.496 | 0.708 | 11 | 5 | 3 | 0 | 0.625 | 17 | 2.224 | ||
| Georgia | 28 | 3.049 | 0.687 | 14 | 5 | 4 | 0 | 0.556 | 7 | 2.494 | ||
| South Florida | 29 | 3.048 | 0.687 | 13 | 4 | 3 | 0 | 0.571 | 11 | 2.370 | ||
| Navy | 30 | 3.001 | 0.685 | 8 | 7 | 3 | 0 | 0.700 | 46 | 1.400 | ||
| Brigham Young | 22 | 22 | 31 | 2.900 | 0.680 | 5 | 8 | 2 | 0 | 0.800 | 71 | 0.853 |
| Boston College | 32 | 2.855 | 0.677 | 9 | 6 | 3 | 0 | 0.667 | 36 | 1.537 | ||
| Arkansas | 33 | 2.826 | 0.675 | 14 | 5 | 4 | 0 | 0.556 | 13 | 2.312 | ||
| Houston | 24 | 24 | 34 | 2.817 | 0.675 | 6 | 7 | 2 | 0 | 0.778 | 63 | 0.939 |
| West Virginia | 35 | 2.665 | 0.666 | 9 | 6 | 3 | 0 | 0.667 | 41 | 1.435 | ||
| Auburn | 36 | 2.379 | 0.648 | 12 | 6 | 4 | 0 | 0.600 | 31 | 1.647 | ||
| Notre Dame | 37 | 2.252 | 0.639 | 12 | 6 | 4 | 0 | 0.600 | 33 | 1.559 | ||
| Mississippi | 38 | 2.228 | 0.637 | 11 | 5 | 3 | 0 | 0.625 | 43 | 1.418 | ||
| Central Michigan | 39 | 2.091 | 0.627 | 6 | 7 | 2 | 0 | 0.778 | 84 | 0.697 | ||
| Nebraska | 40 | 1.994 | 0.619 | 8 | 7 | 3 | 0 | 0.700 | 64 | 0.931 | ||
| Florida State | 41 | 1.985 | 0.618 | 16 | 4 | 5 | 0 | 0.444 | 9 | 2.426 | ||
| South Carolina | 42 | 1.748 | 0.597 | 15 | 5 | 5 | 0 | 0.500 | 28 | 1.748 | ||
| Kentucky | 43 | 1.717 | 0.594 | 14 | 5 | 4 | 0 | 0.556 | 44 | 1.405 | ||
| Oklahoma | 44 | 1.709 | 0.593 | 14 | 5 | 4 | 0 | 0.556 | 47 | 1.398 | ||
| UCLA | 45 | 1.680 | 0.590 | 15 | 5 | 5 | 0 | 0.500 | 29 | 1.680 | ||
| Tennessee | 46 | 1.648 | 0.587 | 15 | 5 | 5 | 0 | 0.500 | 30 | 1.648 | ||
| Minnesota | 47 | 1.549 | 0.576 | 15 | 5 | 5 | 0 | 0.500 | 34 | 1.549 | ||
| Missouri | 48 | 1.498 | 0.570 | 14 | 5 | 4 | 0 | 0.556 | 54 | 1.225 | ||
| Troy | 49 | 1.447 | 0.564 | 8 | 7 | 3 | 0 | 0.700 | 86 | 0.675 | ||
| Texas Tech | 50 | 1.400 | 0.559 | 14 | 5 | 4 | 0 | 0.556 | 57 | 1.145 | ||
| Mississippi State | 51 | 1.372 | 0.555 | 20 | 3 | 6 | 0 | 0.333 | 5 | 2.548 | ||
| Connecticut | 52 | 1.289 | 0.544 | 18 | 3 | 5 | 0 | 0.375 | 19 | 2.026 | ||
| Air Force | 53 | 1.239 | 0.537 | 12 | 6 | 4 | 0 | 0.600 | 70 | 0.858 | ||
| Michigan State | 54 | 1.223 | 0.535 | 15 | 5 | 5 | 0 | 0.500 | 55 | 1.223 | ||
| Washington | 55 | 1.187 | 0.530 | 21 | 3 | 7 | 0 | 0.300 | 6 | 2.543 | ||
| Nevada | 56 | 1.179 | 0.529 | 8 | 7 | 3 | 0 | 0.700 | 95 | 0.550 | ||
| Fresno State | 57 | 1.152 | 0.525 | 14 | 5 | 4 | 0 | 0.556 | 62 | 0.942 | ||
| Northwestern | 58 | 1.151 | 0.525 | 12 | 6 | 4 | 0 | 0.600 | 76 | 0.797 | ||
| UCF | 59 | 1.125 | 0.521 | 14 | 5 | 4 | 0 | 0.556 | 65 | 0.921 | ||
| East Carolina | 60 | 1.061 | 0.510 | 14 | 5 | 4 | 0 | 0.556 | 69 | 0.868 | ||
| Duke | 61 | 1.056 | 0.509 | 15 | 4 | 4 | 0 | 0.500 | 60 | 1.056 | ||
| Arizona State | 62 | 0.993 | 0.499 | 20 | 3 | 6 | 0 | 0.333 | 25 | 1.845 | ||
| Idaho | 63 | 0.961 | 0.493 | 10 | 7 | 4 | 0 | 0.636 | 92 | 0.577 | ||
| Middle Tennessee State | 64 | 0.943 | 0.490 | 8 | 7 | 3 | 0 | 0.700 | 102 | 0.440 | ||
| Southern Methodist | 65 | 0.924 | 0.486 | 14 | 5 | 4 | 0 | 0.556 | 80 | 0.756 | ||
| Iowa State | 66 | 0.874 | 0.477 | 15 | 5 | 5 | 0 | 0.500 | 67 | 0.874 | ||
| Virginia | 67 | 0.820 | 0.466 | 20 | 3 | 6 | 0 | 0.333 | 39 | 1.523 | ||
| Southern Miss | 68 | 0.787 | 0.459 | 14 | 5 | 4 | 0 | 0.556 | 87 | 0.644 | ||
| Texas A&M | 69 | 0.757 | 0.452 | 15 | 5 | 5 | 0 | 0.500 | 79 | 0.757 | ||
| Wake Forest | 70 | 0.757 | 0.452 | 21 | 3 | 7 | 0 | 0.300 | 32 | 1.622 | ||
| Baylor | 71 | 0.738 | 0.447 | 20 | 3 | 6 | 0 | 0.333 | 48 | 1.370 | ||
| Purdue | 72 | 0.736 | 0.447 | 19 | 4 | 7 | 0 | 0.364 | 53 | 1.227 | ||
| Louisville | 73 | 0.726 | 0.445 | 20 | 3 | 6 | 0 | 0.333 | 49 | 1.348 | ||
| Kansas State | 74 | 0.718 | 0.443 | 16 | 4 | 5 | 0 | 0.444 | 66 | 0.878 | ||
| Kansas | 75 | 0.683 | 0.434 | 16 | 4 | 5 | 0 | 0.444 | 73 | 0.835 | ||
| Northern Illinois | 76 | 0.675 | 0.432 | 9 | 6 | 3 | 0 | 0.667 | 108 | 0.364 | ||
| Bowling Green | 77 | 0.624 | 0.419 | 15 | 5 | 5 | 0 | 0.500 | 89 | 0.624 | ||
| Ohio | 78 | 0.624 | 0.419 | 9 | 6 | 3 | 0 | 0.667 | 113 | 0.336 | ||
| Marshall | 79 | 0.612 | 0.415 | 16 | 4 | 5 | 0 | 0.444 | 81 | 0.748 | ||
| Louisiana-Monroe | 80 | 0.578 | 0.406 | 14 | 5 | 4 | 0 | 0.556 | 99 | 0.473 | ||
| Michigan | 81 | 0.577 | 0.406 | 17 | 4 | 6 | 0 | 0.400 | 74 | 0.833 | ||
| Wyoming | 82 | 0.564 | 0.402 | 16 | 4 | 5 | 0 | 0.444 | 85 | 0.689 | ||
| UAB | 83 | 0.511 | 0.385 | 15 | 5 | 5 | 0 | 0.500 | 97 | 0.511 | ||
| North Carolina State | 84 | 0.510 | 0.385 | 22 | 2 | 6 | 0 | 0.250 | 50 | 1.326 | ||
| Syracuse | 85 | 0.476 | 0.374 | 23 | 2 | 7 | 0 | 0.222 | 42 | 1.428 | ||
| Indiana | 86 | 0.407 | 0.349 | 21 | 3 | 7 | 0 | 0.300 | 68 | 0.872 | ||
| Colorado | 87 | 0.390 | 0.342 | 21 | 3 | 7 | 0 | 0.300 | 72 | 0.835 | ||
| Illinois | 88 | 0.380 | 0.338 | 23 | 2 | 7 | 0 | 0.222 | 58 | 1.140 | ||
| UNLV | 89 | 0.363 | 0.331 | 21 | 3 | 7 | 0 | 0.300 | 78 | 0.777 | ||
| Toledo | 90 | 0.324 | 0.313 | 17 | 4 | 6 | 0 | 0.400 | 100 | 0.468 | ||
| Colorado State | 91 | 0.314 | 0.309 | 23 | 2 | 7 | 0 | 0.222 | 61 | 0.943 | ||
| San Diego State | 92 | 0.303 | 0.303 | 20 | 3 | 6 | 0 | 0.333 | 93 | 0.562 | ||
| Kent State | 93 | 0.298 | 0.301 | 16 | 4 | 5 | 0 | 0.444 | 107 | 0.364 | ||
| Louisiana-Lafayette | 94 | 0.273 | 0.289 | 16 | 4 | 5 | 0 | 0.444 | 114 | 0.334 | ||
| Western Michigan | 95 | 0.243 | 0.272 | 17 | 4 | 6 | 0 | 0.400 | 111 | 0.351 | ||
| Florida Atlantic | 96 | 0.242 | 0.271 | 20 | 3 | 6 | 0 | 0.333 | 101 | 0.449 | ||
| Maryland | 97 | 0.226 | 0.262 | 26 | 1 | 8 | 0 | 0.111 | 51 | 1.282 | ||
| Hawaii | 98 | 0.223 | 0.260 | 20 | 3 | 6 | 0 | 0.333 | 103 | 0.413 | ||
| Washington State | 99 | 0.222 | 0.259 | 27 | 1 | 9 | 0 | 0.100 | 45 | 1.403 | ||
| Tulsa | 100 | 0.205 | 0.248 | 20 | 3 | 6 | 0 | 0.333 | 106 | 0.380 | ||
| Louisiana Tech | 101 | 0.204 | 0.248 | 23 | 2 | 7 | 0 | 0.222 | 90 | 0.611 | ||
| Buffalo | 102 | 0.185 | 0.235 | 23 | 2 | 7 | 0 | 0.222 | 94 | 0.555 | ||
| UTEP | 103 | 0.165 | 0.220 | 21 | 3 | 7 | 0 | 0.300 | 110 | 0.353 | ||
| Army | 104 | 0.162 | 0.218 | 20 | 3 | 6 | 0 | 0.333 | 116 | 0.300 | ||
| Florida International | 105 | 0.155 | 0.213 | 21 | 3 | 7 | 0 | 0.300 | 115 | 0.332 | ||
| Tulane | 106 | 0.136 | 0.197 | 23 | 2 | 7 | 0 | 0.222 | 104 | 0.407 | ||
| Memphis | 107 | 0.126 | 0.189 | 26 | 1 | 8 | 0 | 0.111 | 83 | 0.713 | ||
| Vanderbilt | 108 | 0.124 | 0.187 | 27 | 1 | 9 | 0 | 0.100 | 77 | 0.787 | ||
| Utah State | 109 | 0.117 | 0.180 | 23 | 2 | 7 | 0 | 0.222 | 112 | 0.350 | ||
| Akron | 110 | 0.107 | 0.171 | 26 | 1 | 8 | 0 | 0.111 | 91 | 0.606 | ||
| Arkansas State | 111 | 0.106 | 0.170 | 25 | 1 | 7 | 0 | 0.125 | 96 | 0.528 | ||
| Miami (OH) | 112 | 0.105 | 0.169 | 28 | 1 | 10 | 0 | 0.091 | 82 | 0.734 | ||
| New Mexico State | 113 | 0.079 | 0.141 | 23 | 2 | 7 | 0 | 0.222 | 118 | 0.236 | ||
| Rice | 114 | 0.076 | 0.138 | 27 | 1 | 9 | 0 | 0.100 | 98 | 0.479 | ||
| North Texas | 115 | 0.064 | 0.123 | 24 | 2 | 8 | 0 | 0.200 | 119 | 0.218 | ||
| San Jose State | 116 | 0.048 | 0.101 | 29 | 0 | 8 | 0 | 0.000 | 75 | 0.815 | ||
| Ball State | 117 | 0.032 | 0.074 | 26 | 1 | 8 | 0 | 0.111 | 120 | 0.179 | ||
| New Mexico | 118 | 0.019 | 0.049 | 29 | 0 | 10 | 0 | 0.000 | 105 | 0.395 | ||
| Western Kentucky | 119 | 0.019 | 0.049 | 29 | 0 | 9 | 0 | 0.000 | 109 | 0.353 | ||
| Eastern Michigan | 120 | 0.012 | 0.033 | 29 | 0 | 10 | 0 | 0.000 | 117 | 0.250 |
KRACH applied to Division I-A college football
Background
A few years ago I applied Ken's Rating for American College Hockey (KRACH), or Bradley-Terry statistics, to ACHA club hockey teams. At the time, participants for the national tournament were determined by an opinion poll, and there wasn't enough interplay for that to be meaningful (sound familiar?).
In an earlier post here, I intimated that I'd like to see someone crunch the numbers as a mechanism for rating Division I-A college football teams. It's something I've been thinking about for quite some time, just to see what would happen. So tonight I threw something together.
Brief Summary:
"The KRACH rating system is an attempt to combine the performance of each team with the strength of the opposition against which that performance was achieved, and to summarize the result as one number, a "rating", for each team. The higher the rating, the better the team."
"Interpreting the ratings
The ratings are given on an "odds scale": that is, if team A is rated at 400 and team B at 200, team A is reckoned to have odds of 2 to 1 of defeating team B when they meet (since 400 is twice 200). Equivalently, team A is reckoned to have probability 2/3 of defeating team B (since 400/(400+200) is 2/3)."
"There are two things we need to check, to make sure that the rating system is sensible:- If you win more against the same opposition as another team, your rating will be higher.
- If you have the same record as another team, but against tougher opposition, your rating will be higher."
Methods
So, I took the season results from the official NCAA page. I excluded results against FCS competition, as a matter of principle.
One caveat here - I haven't yet worked out what to do exactly with undefeated and winless teams. This will become meaningful at the end of the season if there are multiple undefeated teams (I'm not sure I really care about the winless teams). While I sort that out, I've done the following:
- Verified my calculated rating by calculating the predicted number of wins;
- Determining a percentage difference between the predicted and actual number of wins;
Results
Without further ado, the first KRACH rating for Division I-A college football:
| KRACH | Predicted Wins |
Actual Wins |
% Difference |
||
| 1 | Texas | 200.000 | 8.937 | 9 | 0.702 |
| 2 | TCU | 200.000 | 7.928 | 8 | 0.898 |
| 3 | Boise State | 200.000 | 7.848 | 8 | 1.906 |
| 4 | Cincinnati | 200.000 | 7.830 | 8 | 2.131 |
| 5 | Florida | 200.000 | 7.752 | 8 | 3.104 |
| 6 | Alabama | 200.000 | 8.716 | 9 | 3.160 |
| 7 | LSU | 39.863 | 6.999 | 7 | 0.011 |
| 8 | Georgia Tech | 35.246 | 7.998 | 8 | 0.024 |
| 9 | Oregon | 32.752 | 6.998 | 7 | 0.021 |
| 10 | Iowa | 28.690 | 7.998 | 8 | 0.026 |
| 11 | USC | 21.015 | 6.999 | 7 | 0.021 |
| 12 | Pittsburgh | 17.119 | 6.998 | 7 | 0.024 |
| 13 | Arizona | 14.574 | 4.999 | 5 | 0.025 |
| 14 | Oregon State | 14.533 | 4.999 | 5 | 0.021 |
| 15 | Miami (FL) | 13.562 | 5.999 | 6 | 0.022 |
| 16 | Ohio State | 13.418 | 7.998 | 8 | 0.026 |
| 17 | South Florida | 12.804 | 3.999 | 4 | 0.021 |
| 18 | Penn State | 12.186 | 6.998 | 7 | 0.025 |
| 19 | Virginia Tech | 10.888 | 5.999 | 6 | 0.020 |
| 20 | Clemson | 9.944 | 4.999 | 5 | 0.023 |
| 21 | Wisconsin | 9.061 | 5.999 | 6 | 0.023 |
| 22 | Oklahoma State | 8.788 | 5.999 | 6 | 0.020 |
| 23 | Temple | 7.966 | 6.998 | 7 | 0.026 |
| 24 | Stanford | 7.682 | 5.999 | 6 | 0.021 |
| 25 | Houston | 7.679 | 6.998 | 7 | 0.024 |
| 26 | Utah | 7.215 | 7.998 | 8 | 0.024 |
| 27 | California | 7.194 | 4.999 | 5 | 0.024 |
| 28 | Auburn | 5.098 | 5.999 | 6 | 0.021 |
| 29 | Navy | 4.686 | 6.998 | 7 | 0.026 |
| 30 | Georgia | 4.627 | 3.999 | 4 | 0.019 |
| 31 | Rutgers | 4.399 | 3.999 | 4 | 0.022 |
| 32 | Boston College | 4.292 | 4.999 | 5 | 0.025 |
| 33 | West Virginia | 3.877 | 5.999 | 6 | 0.020 |
| 34 | Tennessee | 3.789 | 4.999 | 5 | 0.018 |
| 35 | Notre Dame | 3.761 | 5.999 | 6 | 0.022 |
| 36 | Arkansas | 3.534 | 3.999 | 4 | 0.022 |
| 37 | UCLA | 3.515 | 3.999 | 4 | 0.016 |
| 38 | Florida State | 3.103 | 2.999 | 3 | 0.019 |
| 39 | North Carolina | 3.030 | 3.999 | 4 | 0.020 |
| 40 | Brigham Young | 2.787 | 6.998 | 7 | 0.025 |
| 41 | Washington | 2.689 | 3.000 | 3 | 0.013 |
| 42 | Central Michigan | 2.345 | 5.999 | 6 | 0.024 |
| 43 | South Carolina | 2.315 | 4.999 | 5 | 0.017 |
| 44 | Minnesota | 2.130 | 4.999 | 5 | 0.023 |
| 45 | Mississippi State | 2.117 | 3.000 | 3 | 0.016 |
| 46 | Fresno State | 2.057 | 4.999 | 5 | 0.025 |
| 47 | Kentucky | 1.951 | 3.999 | 4 | 0.021 |
| 48 | Mississippi | 1.905 | 3.999 | 4 | 0.020 |
| 49 | Arizona State | 1.582 | 2.999 | 3 | 0.024 |
| 50 | Texas Tech | 1.541 | 4.999 | 5 | 0.020 |
| 51 | Northwestern | 1.260 | 4.999 | 5 | 0.023 |
| 52 | Michigan State | 1.219 | 3.999 | 4 | 0.022 |
| 53 | Oklahoma | 1.196 | 3.999 | 4 | 0.017 |
| 54 | Nebraska | 1.172 | 5.999 | 6 | 0.022 |
| 55 | Wake Forest | 1.133 | 3.000 | 3 | 0.015 |
| 56 | Connecticut | 1.010 | 2.999 | 3 | 0.023 |
| 57 | Duke | 0.905 | 3.999 | 4 | 0.025 |
| 58 | Purdue | 0.865 | 3.999 | 4 | 0.018 |
| 59 | Syracuse | 0.836 | 2.000 | 2 | 0.017 |
| 60 | Air Force | 0.729 | 4.999 | 5 | 0.025 |
| 61 | Virginia | 0.719 | 3.000 | 3 | 0.017 |
| 62 | Missouri | 0.718 | 3.999 | 4 | 0.020 |
| 63 | Troy | 0.690 | 6.998 | 7 | 0.022 |
| 64 | North Carolina State | 0.561 | 2.000 | 2 | 0.017 |
| 65 | Kansas State | 0.555 | 3.999 | 4 | 0.020 |
| 66 | Michigan | 0.545 | 3.999 | 4 | 0.023 |
| 67 | Texas A&M | 0.536 | 4.999 | 5 | 0.020 |
| 68 | Baylor | 0.476 | 2.999 | 3 | 0.025 |
| 69 | Idaho | 0.466 | 6.998 | 7 | 0.024 |
| 70 | Iowa State | 0.437 | 3.999 | 4 | 0.023 |
| 71 | Kansas | 0.434 | 3.999 | 4 | 0.020 |
| 72 | East Carolina | 0.413 | 3.999 | 4 | 0.024 |
| 73 | Middle Tennessee State | 0.363 | 5.999 | 6 | 0.022 |
| 74 | Illinois | 0.358 | 1.999 | 2 | 0.026 |
| 75 | Southern Methodist | 0.333 | 3.999 | 4 | 0.022 |
| 76 | Louisville | 0.305 | 2.000 | 2 | 0.020 |
| 77 | Northern Illinois | 0.304 | 4.999 | 5 | 0.024 |
| 78 | Indiana | 0.289 | 2.999 | 3 | 0.023 |
| 79 | Nevada | 0.287 | 5.999 | 6 | 0.022 |
| 80 | Marshall | 0.259 | 3.999 | 4 | 0.021 |
| 81 | Southern Miss | 0.240 | 3.999 | 4 | 0.020 |
| 82 | UCF | 0.223 | 3.999 | 4 | 0.018 |
| 83 | Bowling Green | 0.206 | 3.999 | 4 | 0.024 |
| 84 | Colorado | 0.203 | 2.999 | 3 | 0.025 |
| 85 | Ohio | 0.181 | 4.999 | 5 | 0.020 |
| 86 | Louisiana-Monroe | 0.177 | 3.999 | 4 | 0.018 |
| 87 | Maryland | 0.149 | 1.000 | 1 | 0.021 |
| 88 | San Diego State | 0.147 | 2.999 | 3 | 0.019 |
| 89 | Wyoming | 0.140 | 2.999 | 3 | 0.017 |
| 90 | UAB | 0.134 | 3.999 | 4 | 0.015 |
| 91 | Toledo | 0.117 | 3.999 | 4 | 0.020 |
| 92 | Colorado State | 0.115 | 2.000 | 2 | 0.020 |
| 93 | UNLV | 0.103 | 2.999 | 3 | 0.019 |
| 94 | Kent State | 0.092 | 3.999 | 4 | 0.020 |
| 95 | Western Michigan | 0.088 | 3.000 | 3 | 0.013 |
| 96 | Washington State | 0.074 | 1.000 | 1 | 0.013 |
| 97 | Buffalo | 0.050 | 2.000 | 2 | 0.019 |
| 98 | Louisiana-Lafayette | 0.048 | 3.999 | 4 | 0.016 |
| 99 | Florida Atlantic | 0.036 | 2.000 | 2 | 0.021 |
| 100 | Tulane | 0.035 | 2.000 | 2 | 0.013 |
| 101 | UTEP | 0.033 | 3.000 | 3 | 0.016 |
| 102 | Memphis | 0.031 | 1.000 | 1 | 0.019 |
| 103 | Miami (OH) | 0.031 | 1.000 | 1 | 0.020 |
| 104 | Tulsa | 0.031 | 3.000 | 3 | 0.015 |
| 105 | Akron | 0.030 | 1.000 | 1 | 0.025 |
| 106 | Hawaii | 0.028 | 2.000 | 2 | 0.023 |
| 107 | Louisiana Tech | 0.021 | 2.000 | 2 | 0.019 |
| 108 | Arkansas State | 0.019 | 1.000 | 1 | 0.021 |
| 109 | Florida International | 0.018 | 2.000 | 2 | 0.018 |
| 110 | Army | 0.015 | 3.000 | 3 | 0.013 |
| 111 | New Mexico State | 0.009 | 2.000 | 2 | 0.017 |
| 112 | Utah State | 0.008 | 1.000 | 1 | 0.007 |
| 113 | North Texas | 0.006 | 2.000 | 2 | 0.012 |
| 114 | Vanderbilt | 0.004 | 1.000 | 1 | 0.005 |
| 115 | Ball State | 0.002 | 1.000 | 1 | 0.007 |
| 116 | Eastern Michigan | 0.001 | 0.442 | 0 | 0.000 |
| 117 | New Mexico | 0.001 | 0.162 | 0 | 0.000 |
| 118 | Rice | 0.001 | 0.259 | 0 | 0.000 |
| 119 | San Jose State | 0.001 | 0.006 | 0 | 0.000 |
| 120 | Western Kentucky | 0.001 | 0.216 | 0 | 0.000 |
