Nate Silver and college football

I thought Nate Silver only looked at professional sports. I was wrong – here is a cool interactive web page he has put together for college football. The numbers don’t always give you the answers you want to hear though – even if my beloved Gators somehow win all the rest of their games, which would include beating Alabama in the conference championship game, he gives them only a 13% chance of winning the national championship. Another nice thing about Nate Silver – he always explains his methodology.

We’ll be updating the numbers twice weekly: first, on Sunday morning (or very late Saturday evening) after the week’s games are complete; and second, on Tuesday evening after the new committee rankings come out. In addition to a probabilistic estimate of each team’s chances of winning its conference, making the playoff, and winning the national championship, we’ll also list three inputs to the model: their current committee ranking, FPI, and Elo. Let me explain the role that each of these play…

FPI is ESPN’s Football Power Index. We consider it the best predictor of future college games so that’s the role it plays in the model: if we say Team A has a 72 percent chance of beating Team B, that prediction is derived from FPI. Technically speaking, we’re using a simplified version of FPI that accounts for only each team’s current rating and home field advantage; the FPI-based predictons you see on may differ slightly because they also account for travel distance and days of rest…

Our college football Elo ratings are a little different, however. Instead of being designed to maximize predictive accuracy — we have FPI for that — they’re designed to mimic how humans rank the teams instead.4 Their parameters are set so as to place a lot of emphasis on strength of schedule and especially on recent “big wins,” because that’s what human voters have historically done too. They aren’t very forgiving of losses, conversely, even if they came by a narrow margin under tough circumstances. And they assume that, instead of everyone starting with a truly blank slate, human beings look a little bit at how a team fared in previous seasons. Alabama is more likely to get the benefit of the doubt than Vanderbilt, for example, other factors held equal.

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