Thursday, January 7, 2016

Checking back on point differential predictions

I wrote an entry predicting final season outcomes after week 7, based on point differentials at that point in the season. Let's see how they fared, along with some retrospective notes and commentary.

AFC EastPredictedActualFinal diff
New England Patriots15-112-4+150
New York Jets12-410-6+73
Miami Dolphins9-76-10-79
Buffalo Bills8-88-8+20

All teams were within a game of their differential-based expectations, but they all fizzled in the latter half of the season for various reasons. The prediction of finish order in the division had no material errors, but the Jets did miss the playoff.

AFC NorthPredictedActualFinal diff
Cincinnati Bengals13-312-4+140
Pittsburgh Steelers10-610-6+104
Baltimore Ravens6-105-11-73
Cleveland Browns6-103-13-154

Well, there's a reason Mike Pettine is no longer employed. These predictions were materially spot on: Cinci won the division but missed out on the bye, and Pittsburgh is awarded a wild card berth. Based on differential, we'd normally expect the Steelers to reach 11 wins, but their highly bipolar games (with vs without Roethlisberger) explain that outcome.

AFC SouthPredictedActualFinal diff
Indianapolis Colts6-108-8-75
Tennessee Titans6-103-13-124
Houston Texans5-119-7+26
Jacksonville Jaguars4-125-11-72

The Texans turned their season around as effectively as they jettisoned Ryan Mallett. Clearly he was not the answer, and going to Brian Hoyer was the trick. The Colts stayed right on track in point differential, but managed to squeeze 2 unexpected wins out. The Titans and Jags underperformed their expectations by 1 game each. This division went completely against projections, though a statistician would argue that there was a lot of noise in the signal in Week 7. All the teams looked bad, there was no way to guess who would get their act together.

AFC WestPredictedActualFinal diff
Denver Broncos11-512-4+59
Oakland Raiders7-97-9-40
Kansas City Chiefs6-1011-5+118
San Diego Chargers6-104-12-78

Who saw the Chiefs coming back to win 9 of their last 10 without Jamaal Charles? Seriously, that's crazy. The really crazy thing is their point differential puts their expectation just slightly towards 12 wins! Denver, on the other hand, outperformed their differential by 2 wins. I'm proud of the projection though, it's meaningful to project that a 6-0 team will be barely over .500 the rest of the way. The Chargers battled hard and we'd normally expect to see 6 wins at -78 points, but they just couldn't close out games. The projections correctly identified the division winner, but missed on the wild card.

Overall in the AFC, we correctly predicted 3 division winners and 1 wildcard (though to be fair, none of those predictions was a stretch), and a total of 4 playoff teams correctly.

NFC EastPredictedActualFinal diff
Philadelphia Eagles10-67-9-53
New York Giants9-76-10-22
Washington Redskins7-99-7+9
Dallas Cowboys5-114-12-99

The two teams that looked to be the favorites imploded down the stretch and are now searching for new coaches, and somehow Kirk Cousins channeled his inner Drew Brees. Redords are all within a game of where differential expects; everyone but the Cowboys changed course in the back half. The Cowboys ... well. The projections missed on the division winner, but correctly predicted no wild card teams. That counts for something, right?

NFC NorthPredictedActualFinal diff
Green Bay Packers13-310-6+45
Minnesota Vikings10-611-5+63
Detroit Lions4-127-9-42
Chicago Bears3-136-10-62

Projections identified both playoff teams (though the Vikings were in the maybe bucket with Atlanta), just in reverse order. This wasn't a stretch either. The Bears and Lions turned in respectable second halves, and the Packers completely underperformed. Records are where we'd expect them to be based on differentials.

NFC SouthPredictedActualFinal diff
Carolina Panthers12-415-1+192
Atlanta Falcons11-58-8-6
New Orleans Saints6-107-9-68
Tampa Bay Buccaneers5-116-10-75

A clean sweep! Remember at the time that many were doubting the Panthers despite their perfect start. They actually outperformed expectations at the end, +192 would project to 14 wins; they made a really strong run at 16-0. Differential at the time correctly predicted Atlanta's decline, but even it wasn't detached enough to see a 2-7 finish and missing the playoffs coming.

NFC WestPredictedActualFinal diff
Arizona Cardinals14-213-3+176
Seattle Seahawks10-610-6+146
St Louis Rams7-97-9-50
San Francisco 49ers3-135-11-149

Another really good projection! We nailed the division winner and the wildcard. Records were right where final differentials would expect, except for the 49ers who really had the differential of a 3-13 team but pulled some miracle version of Blaine Gabbert from their bench.

Overall in the NFC, we hit 3 of the division winners and 1.5 wild cards (calling Falcons/Vikings a 50/50), but overall got 5.5 of the playoff teams right.

For the NFL as a whole, using point differential after week 7 to predict final outcome was reasonably good. The method picked 6 of the 8 division winners and 9 or 10 of the 12 playoff teams. The method of using point differentials isn't anything earth-shattering or super insightful. The interesting question here is if representative data is present after 7 weeks. The answer seems to clearly point to yes.

The appeal of the method is its simplicity. It requires no complex math, no models adjusting for strength of schedule or opponents; it's something anyone can use in their head or on a napkin. If I felt up to it, I'd do an analysis of how many playoff teams are correctly predicted as a function of number of games played. Any strong indicators could be useful, say, in Vegas.

Per differential, the Panthers are favored in the Super Bowl. The Cardinals are 2nd and the Seahawks barely trail the Patriots for 3rd. Adjusting for injuries and when teams are peaking (or flailing), and it really seems like the top 3 contenders are from the NFC.

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