Do Older Quarterbacks Wilt In December and January?

In Aaron's appearance on the B.S. Report [1] (a free-flowing conversation that occasionally touches on mature subjects) this week, Bill Simmons asked us to analyze whether aged quarterbacks wilt in the winter months, their creaky bones too brittle for the 16-game schedule.

While Bill suggested that we put the answer in PFP 2009, this is exactly the sort of question the fantasy database that I use to project matchups each week has a readily-available answer to. While we don't have 2008 data in there as of yet, we can look at how quarterbacks have fared over the 13 years of game-by-game data we've compiled for the database already.

The data set here is every instance of a quarterback throwing 10 or more passes in a game from 1995 through 2007. The quarterback's age is defined as whatever his age was on September 1 of the season in question.

Of course, defining the age at which a quarterback is old is a difficult enough question. The 90th percentile of quarterback age amongst the 6500 games in the study is 35, so we'll define quarterbacks 35 and older to be the quarterbacks in question. I wanted to do this quickly, and the fantasy database doesn't have game-by-game DYAR, so we'll use quarterback rating as the measure.

Let's split the months to compare how a quarterback does in December and January (regular season games only) as opposed to how he does in the rest of the regular season. We'll split the remaining quarterbacks a couple of different ways.

Those elderly quarterbacks are losing more in the way of quarterback rating than their younger brethren, but that's because they gain more points during the warmer months than those quarterbacks do. That's due to selection bias: The quarterbacks who have made it as professionals to the age of 35 are a more talented, successful group of quarterbacks than the broader pool of quarterbacks who enter the league and play from the ages of 21 to 34.

If we measure the effect of the colder months as a percentage of their average quarterback rating in the previous months, old quarterbacks suffer from the cold weather and strain of a season almost identically as much as the broader pool. The difference is less than one-tenth of one percent.

In other words, while old quarterbacks play slightly worse at the end of the season, it's a trend that has nothing to do with their age.