After watching years of football games, I am always left
feeling that either team could have scored another touchdown or that either
team got lucky and scored a touchdown they didn’t deserve. The BSC also acknowledged this and moved to
get the margin of victory removed from their polls. However, this over rewards teams who just
barely won. Rather, close games indicate teams that are of equal or near-equal strength. The other argument against margin of victory
is that blowouts are over-rewarded. By computing the odds of winning through a
power number and a Pythagorean of the score, the effect of blowouts is merely
to distinguish that the winner is superior.
If the score is only used as an approximate and is adjusted to allow an
additional score by either team, then the ratings should also avoid the
difficulty in ranking teams in close games.
The details of the method are given below.
Here is a brief summary of how the ratings are determined.
- Assume
that the odds of winning a game are described by a Pythagorean calculation
of the games score:

- Compute
a window of the odds by adding 7 points to A’s actual score and then by
adding 7 points to B’s actual score.
(saying that either team could have
reasonably scored another touchdown and PAT).
- Determine
the odds of winning based on a probability number:

- subtract
the odds computed in 3 from that computed in 1 and square the result
- If the
odds computed in 3 are outside the range computed in 2 ten multiple 4 by
five. Else multiply by one.
- Minimize
the sum of the computations in 5 for all games simultaneously.
- This
is aided by making a variable substitution such that
, which results in 3 being
and has the
benefit of w being unbounded. Then minimization can be done via a Jacobean
(Newton-Raphson) iteration.
Some side notes:
- Home
field advantage: Because I only use the score as approximate, it is not
necessary to account for home field advantage. Other models that do so only attribute 2
-3 points for home field. Since the
scores are considered to be within 7 points of a reasonable value, the
home field advantage can manifest itself without explicit determination.
- Divisional
Strength: Most methods of computing divisional strength are ad hoc
adjustments. Meaning that they are
not necessarily based on a model of how the strength between teams is
determined, but added to avoid the instances when a team dominates their conference
but the teams in that division were dominated by teams outside the conference
as well. Obviously, the challenges
of playing in a major conference are tougher than
playing in a small conference.
However, without actual game results, there is no means of discerning
if the weakness of the conference yielded the dominance of a good team, or
if the team was great and would have dominated any conference. Likewise, is a poor team in a good
conference really better than a poor team
in a poor conference? All the data
simply says the team was easily beaten by all opponents. For this reason, I do not attempt to
adjust for conference strength. This can lead to disputable results, but
any adjustments would make the results equally disputable.
- Is this
a predictive model? The nature of a computer ranking model is to determine
which team is better when the two haven’t played (or when they have
played, but the result was not consistent with the other games played).
Thus, all ranking models are predictive regardless of if they attempt to
determine the score of a future game or simply run a formula based on past
performance. Given this, I will
argue that computer ranking schemes that attempt to make accurate
predictions of future outcomes are better than
those which take a more simplistic and retrospective approach.
- Problems
with computer ranking models: Almost
every computer ranking schemes limit their input to the final outcome and
possibly the home team. This
assumes that the team ability is constant from game to game throughout the
season. There is no account for
weather effects, key injuries, unique weaknesses
in certain philosophies that certain opposing philosophies are designed to
exploit, luck, etc. With such
limited input, we should not expect the rankings to be all that
precise. I would say that it can distinguish
a great team form a good team from a poor team from a terrible team. The exact ranking is not able to be
determined with such limited input.
To account for all factors would require precise simulation of
every possible game several times.
Even advanced game simulations (think Playstation
games) are limited in their accuracy to reproduce the different play
calling options and outcomes. So, a
ranking scheme presented here or elsewhere is not accurate. They are reasonable in that they produce
a ranking that completely accounts for all inputs equally. There are approximately 1400 division 1A
football games each season. To
learn enough to properly evaluate all of them would be a daunting task for
any human. In light of this,
computer rankings give a good starting point to the rue ranking and this
can be balanced with some thoughtful analysis on the part of humans.
- NCAA
Division 1A playoffs vs. the current bowl system: The current bowl system
acts as a 2 team playoff with rewards for nearly every team with a wining
season. This works well in terms of scheduling and interest. How many teams would have a large
following through several rounds of a playoff system? Would the fans of
teams that were no longer involved care about the playoffs? Would a better champion be
determined? I’d like to address
this last question. If two great
teams play, the odds of one winning are likely limited to 60%, maybe 75%
if the team is that awesome. So,
the better team can always be upset if it plays a quality opponent. If more games are played against quality
opponents then the chance that the
strongest team is the champion is reduced.
This is why the NCAA basketball tournament can have frequent Cinderella
stories. You may argue: If the team
won then it was truly the stronger team.
That may or may not be true.
If you watch a game, you can often argue that luck, bad
officiating, or a single botched play caused the score to be in favor of
the opposing team. If these are
real factors, then the strongest team does not always win. So, a playoff does not produce a better
champion. It does reduce the
opportunity to argue the merit of the champion because it at least won a
series of games. I would prefer to use the season as a playoff culminating
in a championship game with other good teams getting to go to bowl
games. I’ll post more details on
this at a later date. Given the choice
of a playoff system or a bowl system, I am very happy with the bowl system
and hope that it is retained.