"You are what your record says you are."
Bill Parcells' famous quote about the NFL brilliantly expressed the importance of not making excuses and playing the "what if" game in an NFL locker room. Teams win and lose games, and all the justification in the world doesn't change that.
Unfortunately, Parcells' truism is also completely useless for understanding what is going to happen in the future. This week's advanced stat is Pythagorean Wins.
The concept is simple, even though the math is tricky. The idea is that over time, a team's point differential (points scored minus points allowed) is a better indicator of how that team will perform in the future than their record is.
For example, a team that is 6-2, but has been outscored by five points on the season because of a couple of blowout losses, is more likely to play like a 4-4 team going forward than like a 6-2 team.
While fans like to point to a team's record and crow, often times there are warning signs that the luck is about to run out. The same can be true for a struggling team that has actually outscored opponents on the season. This relationship between future wins and point differential is not debatable.
For the purposes of projection into the future, you are better off looking at Pythagorean Wins than real wins. The 2010 Packers won 10 games on the field, but were dominant on the field, leading the NFC in point differential. They weren't really a 10-win team sneaking into the playoffs on tiebreakers. They were really a juggernaut with some bad luck. The playoffs revealed the truth.
There are many different ways to calculate this number, but they all are based on essentially the same components—"points for" and "points against." This can be a handy tool for predicting a big fall from a team with a good record, or a big leap forward from a team that had some bad luck. No statistical tool is right all the time, but Pythagorean Wins has a good track record, and is far more useful than actual wins for predicting the future of a team.
The Jacksonville Jaguars are a great team to use to help understand Pythagorean record. In 2011, the Jags were outscored by 86 points on the season. By Pythagorean record, they were a 5.2 win team. Lo and behold, the Jags actually won five games. In this case, they performed according to expectation.
Let's roll the clock back a year to the Jaguars' surprise 2010 run at the playoffs. Jacksonville went 8-8, but at one point in the season were 8-5 and only needed a win at Indianapolis clinch a playoff berth. Even so, many analysts refused to take the Jags seriously. Why?
The Jaguars had a number of miraculous, close wins in 2010. Even as their real record stood at 8-5, they had been outscored by 36 points on the season. Remember, that you aren't what your record says you are. The Jaguars weren't as good as their record indicated. Pythagorean wins said their record should have been closer to 6-7. Sure enough, they lost the last three games of the season.
Looking forward to 2011, fans had a choice. They could see the Jags as a team on the verge of contention because of the hot start and near division title, or they could see the Jags more like a 5 or 6 win team.
Pythagorean Wins suggested the Jaguars were primed to regress back toward double-digit losses. That's exactly what happened in 2011.