Wednesday, October 21, 2015

The Return Of SORTACUS

Last year I applied an algorithmic program named SORTACUS to rank college football teams.  SORTACUS was created in tandem by Andy Meisner and me during our grad school suffering.  Although originally written to help Andy rank his favorite movies, it applies well to college football.  With most teams seven games into the season, I thought it was time to put SORTACUS to work again.

SORTACUS and the College Football Playoffs

I've long had a fascination with the college football postseason, something I treated in detail a few years ago during BCS Week.  I believe that playoff appearances should be determined by an algorithm to calculate which team is most deserving (based solely on wins and losses).  This is done in nearly all sports, but due to the nature of college football it needs to be a more complex algorithm.  After years building and examining ranking systems, I think SORTACUS is optimal for this task.

SORTACUS is an entirely algorithmic ranking system based solely on wins and losses.  It relies on Bayesian statistics, using a prior rating and each game as an observations to calculate a posterior ratings distribution.  I haven't given a full description yet, but last year I shared a few more details of SORTACUS.

It's important to note that SORTACUS is designed to rank teams in order of performance so far.  In effect, this calculates which teams are most deserving of being in the playoffs.  If you instead want to predict which teams will win in the future, check out my work with TeamRankings.

Top 25

The experienced readers likely just jumped straight to these ratings.  Below is the SORTACUS top 25 using games through Saturday.  In theory, the top 4 teams are the most worthy of a playoff spot so far.  Note that only FBS vs FBS games are considered (affecting the record totals), and that "Rating" corresponds roughly to how many points better than the FBS average a school has been.

Rank Team Record Rating
1  Utah 6-0 21.60
2  LSU 6-0 20.52
3  Iowa 6-0 20.47
4  Michigan St 7-0 19.94
5  Ohio St 7-0 19.03
6  TCU 6-0 18.63
7  Clemson 5-0 18.59
8  Memphis 5-0 17.66
9  Florida 6-1 16.57
10  Oklahoma St 5-0 16.27
11  Baylor 5-0 16.10
12  Florida St 6-0 16.10
13  Temple 6-0 15.86
14  Notre Dame 6-1 14.97
15  Alabama 6-1 14.94
16  Toledo 6-0 14.64
17  California 4-1 14.61
18  Houston 5-0 13.76
19  Michigan 5-2 12.92
20  Texas A&M 5-1 12.89
21  Stanford 5-1 12.60
22  Northwestern 4-2 11.51
23  Oklahoma 5-1 11.33
24  Washington St 4-1 10.48
25  Pittsburgh 4-1 10.12

Through October 17th the 4 teams most deserving of a playoff spot are Utah, LSU, Iowa, and Michigan State, with a gaggle of undefeateds looking on.

Wait.

What?

IOWA IN THE PLAYOFFS?!?!?!

That's right, as of now the Iowa Hawkeyes are the third most accomplished team in college football.  They have four surprisingly good wins against Northwestern, Pittsburgh, Wisconsin, and Illinois.  The Hawks have a weak schedule going forwards, and are ranked only 31st in TR's predictive rankings.  For now though, Iowans have reason to celebrate.

Outside of Iowa the rankings follow roughly as expected.  Utah has taken college football by storm so far, and is clearly deserving of it's top spot.  One loss teams like Florida, Notre Dame, and Alabama are ahead of some undefeated squads, and absolutely still have a chance to finish the year on top.  It's all setting up for a fun fall.

How Is My Team Doing?

Not everybody gets to be a fan of the 3rd most successful team in the country.  For the less fortunate, some notable team rankings are listed below.
Texas Tech:  37th, rating of 6.17
Auburn:  38, 6.12
Nebraska:  65, -0.52
NC State:  70, -2.07
Maryland:  82, -5.47
Iowa State:  83, -5.70
Purdue:  121, -15.81
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