Posted by Doug on June 18, 2007
First, it's been awhile since I plugged The Audible. Right now they are, among other things, having fifteen-minute conversations with beat writers from each NFL team. If you've got a commute or if you listen to headphones while you get your exercise in, The Audible makes ideal listening material.
And in particular, I got an idea as I listened to the interview with Colts' beat writer Mike Chappell from the Indianapolis Star. Chappell mentioned that, because they had such a long season last year, the Colts have been taking it easy during the offseason. Coach Tony Dungy has given them more time off and has made practices less intense.
Part of the curse of being me is that I am totally incapable of hearing something like this without trying to set up some sort of study on it. We know NFL teams that win a lot of games in Year N tend, as a group, to decline in the Year N+1. Part of that is due to regression to the mean, a phenomenon that transcends football. Part of it might be due to the structure of the NFL: the salary cap making it harder to keep star players, having the last draft slot, and so on. But might part of it be also due to the fact that Super Bowl teams play more games and have a shorter offseason?
From what I can gather, football can be a physical game. I don't think it's unreasonable to suggest that a team that has six months to recover from a 16-game season has an advantage over one that has five months to recover from a 20-game season.
Of course teams that play 19- or 20-game seasons will tend to do better the next year, as a group, than teams that play 16. Here is a meaningless chart that confirms that:
Playoff games played Year N Av Wins Year N+1 ================================================= 0 7.3 1 8.8 2 9.1 3+ 10.3
But that's to be expected. It's simply another example of causation and correlation not being synonymous. Year N+1 wins are not caused by playing playoff games in Year N. Rather, both of them are caused by the same unnamed factor: being good.
But the interesting (to me, that's who!) question is: given two teams with the same number of regular season wins in Year N, does the one that played more postseason games in Year N figure to do better than, worse than, or the same as the team that played fewer?
Answer: the same. More specifically, if your intuition tells you that "the same" was the right answer, then there is nothing in the data that should cause you to seriously re-consider that. In particular, here is what I did. I looked at all pairs of seasons starting in 1978 (the first year of the 16-game schedule), not counting pairs that included a strike year. For each number of wins starting at 9, I looked at all teams with that number of regular season wins in Year N and then ran a regression of Year N+1 wins versus Year N postseason games played.
For no group of teams did the input variable appear to be significant. For what it's worth, the coefficient was positive for most groups of teams. For example, here are the results for the 12-win group:
Year N+1 wins =~ 8.14 + .58*(postseason games played in Year N)
So based on what the data shows for 12-win teams, every playoff game played in Year N is associated with .58 more wins in Year N+1. But as I said above, that .58 is probably not big enough to infer a real effect, in the same sense that you probably wouldn't conclude that a coin was biased if it came up heads 56 times out of 100, unless you already had some other reason to believe it was biased.
Age, offseason movement, schedule strength, and countless other factors obviously play roles here too, and they haven't been accounted for. This was just a quick check and it failed to find evidence for a tiring factor, perhaps because Super Bowl coaches like Dungy adjust their teams' schedules accordingly.