"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 Houston Texans jumped up on people last year. For years, prognosticators were picking the Texans to make the leap to the next level, but they always finished around .500, disappointing the media and fans alike. Last year, it all finally clicked.
Thirteen games into the season, the Texans were not only leading the AFC South, but the entire AFC as well. While it was a bit of shock, there was every indication the Texans were absolutely for real. Their record was 10-3 but, just as importantly, they had outscored opponents by 122 points. A big scoring differential is a good indication of overall team strength.
The math confirmed the Texans' record at that point of the season. By "expected" or "Pythagorean wins," the Texans were at 9.7 wins, exactly where their record stood.
Houston slumped over the final three games of the season due to injuries and lost the final game of the year to the Tennessee Titans in part because Gary Kubiak rested players for the playoffs. For the season, the Texans' expected record was 11-5 (mathematically 10.9-5.1), and their actual record was 10-6. If not for the decision to rest so many starters, the Texans would likely have hit their expected wins total on the nose.
In this case, Pythagorean wins are a comfort to Texans fans. There was nothing fluky or lucky about the Texans' run to the playoffs. It was the result of a good offense and a good defense. Their point differential was third best in the AFC, which is essentially where they finished after a loss to the Baltimore Ravens in the second week of the playoffs.
Looking toward next year, it's best to think of the Texans as an 11-win team and to adjust expectations up or down from there based on the results of the draft and free agency.