Posted by Doug on October 2, 2007
Back before the college football season started, I mocked the human polls and devised an algorithm to mimic them. I still haven't gotten around to catching up with what that "poll" would look like for the 2007 season, but I promise that I will do that at some point before too long. (<--- Promise #1) Even without running it, though, it does seem clear that my algorithm isn't going to be as accurate as I hoped. So here I am admitting I was wrong. My apologies to all those graduate assistant strength-and-conditioning coaches and newspaper sports page interns. They have indeed been giving their rankings a bit more thought than I was giving them credit for. Promise #2 is to someday (within the next two weeks) do the programming for a new rating system that I'm about to tell you about. I'm hoping that putting the promise in writing will make me more likely to keep it. It starts with a comment that was recently added to one of my old rating system posts, and is similar to other comments on rating systems. I can't find it at the moment, but I'll paraphrase it:
Does this system take into account the strength of the team at the time? For example, if the Patriots suffer some injuries and end up 8-8, then the Jets, Chargers, and Bills should get credit for losing to a great team --- a team that truly was playing lights-out at the time --- rather than some generic 8-8 team.
I think arguments could be made both fer and agin' that mode of thinking, but I'm going to set them aside for now and focus on the question: assuming you do want to incorporate at-the-time strength of opponents into your rating system, how do you do it?
Measuring at-the-time strength of schedule instead of overall strength of schedule necessarily means that you are treating the Week 2 Patriots as a different team than the Week 14 Patriots. It's possible, I'd even say likely, that both of those teams are of similar strength, but we don't want to assume it. If you take this thinking to its extreme, then you'd have to assume that there is no team called the "Patriots." Rather, there are 16 Patriot teams, one for each week. There may be some correlation between their strengths, but if you really want to go all the way with the at-the-time SOS philosophy, you can't assume it. And I guess that leaves you making no strength of schedule adjustments at all.
OK, so we don't want to be that extreme. If we're to conclude anything at all about strength of a team's schedule, we have to make some sort of assumption that every team bears some resemblance to its incarnation of the previous week, and of the next week. Consider this:
Week 1: Vikings over Falcons by 21 Week 2: Jags over Falcons by 6 Week 3: Panthers over Falcons by 7 Week 4: Falcons over Texans by 10
If we assume the minimum amount of continuity between the possibly-different teams that took the field wearing Falcon jerseys --- that is, if we want to allow the possibility that the Falcons' strength is continuously in flux --- then we don't want to infer too much about the relative strengths of the Vikings and Texans by comparing how they did against the Falcons. Those were different Falcon teams, after all. The minimum amount of continuity would be one game, so let's compare Falcon opponents only if they played the Falcons in consecutive games. So I can compare the Vikes to the Jags via the Falcons, and I can compare the Panthers to the Texans via the Falcons, but I won't (directly) compare the Vikings to the Texans.
Over the years I've learned that the simple rating system can do just about anything you want if you just figure out how to redefine what a "game" is. So I propose to regard this data as follows:
The Vikings are 15 points better than the Jags The Panthers are 1 point better than the Jags The Panthers are 17 points better than the Texans
Those are my games. And likewise there was a "Falcons-Lions game," which the Lions won by 24 points (do you see why?), and a "Falcons-Titans game," which the Titans won by 3, and so on.
And then I'll run the simple rating system on this collection of games. As you can see, there will still be an implied connection between the Week 1 Falcons and the Week 3 Falcons, but it will be indirect. And the connection between the Week 1 Falcons and the Week 17 Falcons will be so indirect as to be practically meaningless.
You need not write in to tell me that this is a pointless academic exercise; I already know that. But pointless academic exercises are my schtick, so I'm going to roll with it. I'm under no illusion that this will provide a better rating system, but I do think that, by taking a look at the teams whose traditional simple rating are very different from what this rating shows, we might find out some interesting things that we didn't know before.