Thursday, July 26, 2007

Who's On the Rise and Who's On the Decline: Expanded and Corrected

Going over the 2007 Pro Football Prospectus, I thought I'd give a quick shot at predicting whose win totals would improve/decline next season.

I chose the linear regression model of season win totals based on Value Over League Average, training on 1996-2005, and took a look at which teams won at least X more/fewer games than their expected win totals, where X was the mean absolute error on the 2006 season (1.233 games). So the rule of thumb is that those who won ≥1.233 games less than their expected win total is expected to improve in 2007. Those who won ≥1.233 games more than their expected win total is expected to decline in 2007.



IMPROVE


  • Miami Dolphins (7.9975 expected wins, 6 actual) Very good defense with gaps in the secondary and an aging core. Offense will hopefully improve with a good quarterback (Trent Green), but the receiving corps is weak. The offensive line is also being reshuffled. Any statistical improvement will likely be regression to the mean as much as actual increase in talent.
  • Pittsburgh Steelers (9.4697 expected wins, 8 actual) Big Ben will be healthy. That should make all the difference.
  • Jacksonville Jaguars (10.432 expected wins, 8 actual) They need to settle on a quarterback because otherwise, this is a very good team. Their unadjusted VOLA for run offense and defense are 20.0084% and 16.382% (percentage above league average for yards per carry). Their pass efficiency was below average on defense, but they got a lot of interceptions (their rate was 21% above league average). I will jump on the FO bandwagon and peg them as the big sleeper of 2007.
  • Oakland Raiders (4.1932 expected wins, 2 actual) There's nowhere to go but up, right? Well, actually, their pass defense was good (9.04%, 15.775% unadj VOLA in pass eff. and sack rate made). It's just that their pass offense was far more atrocious (-27.022% pass eff., -96% sack rate allowed, a sack rate of 11.6% compared to a 6.2% league average). Don't expect them to be playoff contenders, but if JaMarcus Russell and Michael Bush are simply mediocre, this team is at least a 5 or 6-win team.
  • Philadelphia Eagles (11.294 vs. 10) If not for a freak 62-yard game winning field goal (Matt Bryant of the Bucs), the Eagles wouldn't be in this list. The Eagles might not improve their win total in 2007, depending on when McNabb is able to play effectively again. Despite the injury to McNabb, their pass efficiency was 20.58% above average in 2006. They went 1-3 against the AFC South and don't look to fare much better against the AFC East in 2007. They do, however, play the NFC North instead of the South. My intuition is that their interdivision and interconference games will be the difference between 10-6 and 13-3.
  • Detroit Lions (5.2434 vs. 3), Minnesota Vikings (8.0195 vs. 6) I don't expect them to be significantly better. I just expect the Bears to be worse.


DECLINE

  • New England Patriots (10.013 vs. 12) With a legitimate wide receiving corps (that is quickly becoming the most overrated without having played a down), I wouldn't buy into this. New England will do just fine.
  • New York Jets (8.3734 vs. 10) Their defense just isn't very good. And their passing game was average. This is a team I'd expect to regress to the mean. Thomas Jones is a good back, but I don't think that's enough to make this team a legit playoff contender.
  • Tennessee Titans (4.6593 vs. 8) When you're winning games with 62 yard field goals, you know your luck is good. But they've lost Pacman Jones, and how many times can they rely on Vince Young's scrambling ability?
  • San Diego Chargers (12.401 vs. 14) I think that this will happen with most 14 or 15-win teams. It's not that the Chargers weren't very good. They were at least 10% above average in rush offense, pass offense, and pass defense efficiency. It's just that with "luck" and scheduling, teams have to be really, really, super good for the system to guarantee at least 14 wins. That said, they play the AFC South and NFC North this year, as opposed to the NFC West and AFC North, so expect some drop off in win totals.
  • Chicago Bears (11.005 vs. 13) The Bears were lucky to play 4 games against the NFC West. Next season, their intraconference matchups will be against the NFC East, plus the Saints. A harder schedule will mean fewer victories. That said, Rex Grossman's passing efficiency was about average, and the pass defense was very good. Actually, Rex Grossman and the offensive line did a very nice job of avoiding sacks as well. Thomas Jones, according to these numbers, was overrated, as his efficiency was 8.69% below average. So was my original perception about Rex Grossman being crappy wrong? I don't think so. I think the weak schedule might have inflated his numbers somewhat (adjusted VOLA is about 0% as opposed to about +2%). I'd peg them down as an 9-7 or 8-8 team. Somebody has to win the NFC North, after all.
  • Atlanta Falcons (5.5363 vs. 7) Great offense rushing efficiency (31% VOLA) but a very bad pass offense (-14.45% VOLA). Bad pass defense too. With Joey Harrington under center, don't expect their pass efficiency to go up much, if at all. They might get some help from playing the NFC West.
  • San Francisco 49ers (5.2197 vs. 7), Seattle Seahawks (6.906 vs. 9) This is really just a result from the NFC West being a really weak division overall. The Cardinals drew the shortest straw in 2006 apparently. While Seattle also had health issues dragging down their season averages, Shaun Alexander might not recover so easily from overuse in 2005.


The numbers don't seem to add much to what we already know, but it will be interesting to see how the predictions will play out. At the end of the season, I'll pick apart the article and methods to see what went right and what went wrong. I think the running theme of the article, however, is that the quarterback is the key issue for most of these teams. For some teams, other team's quarterbacks seem to be the issue.

In short: The NFC North and NFC West are mediocre but wide-open divisions. Atlanta might miss Michael Vick, but the Falcons weren't very good before he got himself in legal trouble. The Steelers and Eagles can expect improvment with healthy quarterbacks at the helm. Jacksonville has great potential to get deep into the playoffs. Chicago is going to sink in 2007. And Tom Brady and Bill Belicheck must be pretty dang good to perform so well with Reche Caldwell and Jabar Gaffney as their receivers.

Addendum: Accuracy of Rise and Fall Projections
I went back and checked tested these rise-and-fall predictions on the 1997-2005 seasons against each selected team's win total the following season. Over those 9 seasons, 53.125% of predicted risers saw at least a 1-game increase in win totals the next season, while 62.295% of predicted fallers saw at least a 1-game decrease in win totals. Over 2002-2005 (the last realignment), however, the accuracy numbers were 65.517% and 67.742%. So the divisional realignment and new scheduling method seem to expose more teams with abnormally high or low win totals as the bad/good team they actually are.

For one more experiment, let's try projecting next season's win totals based on expected and actual wins as a simple regression model. The inputs are actualwins(Y) and expectedwins(Y)-actualwins(Y) and a bias input (always equal to 1). So the idea is that teams that outperform projections will be penalized and teams that underperform will be rewarded. The output will be actualwins(Y+1).

This model, unsurprisingly, isn't very good. The mean absolute error was 2.1299 games in predicting actual wins in 2006. The correlation coeffecients to actualwins(Y+1) are 0.26804 for actualwins(Y) and -0.0052895 for expectedwins(Y)-actualwins(Y). I was surprised to see the second coefficient close to zero. The difference between expected wins and actual wins is actually the error of the win total regression system, and that error goes both ways creating "random" noise. The error doesn't necessarily mean that team over or underperformed that season. That is only the interpretation I ascribe to it (and as a side note: I think it's important to state that statistics are merely tools. They can be poorly designed or poorly implemented. I think people are too quick to dismiss stats as excluding intangibles. That is the interpretation they've ascribed to the stats. It may or may not be true.).

The regression coeffiecients make a little more sense, however. Each win in year Y is worth 0.29507 wins in year Y+1. Each expected win a team did not get in year Y is worth 0.17917 wins in year Y+1. Each win above the expected win total in year Y is worth -0.17917 wins in year Y+1. Each team is automatically "given" 5.6739 wins (the coefficient for the bias input). For the predictions next year, I swapped out the actual wins input with expected wins in 2006. This was an inadvertent mistake on my part and not completely sound science. However, the predictions are more interesting this way. One of the weaknesses of many next-season win projections is that division rankings aren't shaken up very much, if at all. This slip-up turns out to be pretty useful because it does mix things up. All of the predicted win totals for 2007 are between 6-10 games, so the exact predictions are not very useful. The rankings, however, are useful. Here are the expected final intradivision rankings for 2007.

AFC East

  1. Miami Dolphins
  2. New England Patriots
  3. Buffalo Bills
  4. New York Jets


AFC North

  1. Baltimore Ravens
  2. Pittsburgh Steelers
  3. Cincinnati Bengals
  4. Cleveland Browns


AFC South

  1. Jacksonville Jaguars
  2. Indianapolis Colts
  3. Houston Texans
  4. Tennessee Titans


AFC West

  1. San Diego Chargers
  2. Kansas City Chiefs
  3. Denver Broncos
  4. Oakland Raiders


NFC East

  1. Philidelphia Eagles
  2. Dallas Cowboys
  3. New York Giants
  4. Washington Redskins


NFC North

  1. Chicago Bears
  2. Green Bay Packers
  3. Minnesota Vikings (1,2, and 3 are very close)
  4. Detroit Lions


NFC South

  1. New Orleans Saints (by a mile)
  2. Carolina Panthers
  3. Tampa Bay Bucs
  4. Atlanta Falcons


NFC West

  1. St. Louis Rams
  2. Arizona Cardinals
  3. Seattle Seahawks (1, 2 and 3 are very close)
  4. San Francisco 49ers


Certainly, I disagree with some of these projections, but a lot of my assumptions at the beginning of the season don't pan out, so I'll see how the numbers do.

7-30-07: I found an error in my offensive pass efficiency stats. Results and article corrected.
7-30-07: Added section to article about accuracy of this projection system.
8-27-07: Corrected NFC North order and prediction method.

8 comments:

Brian Burke said...

I'm seeing the same improve/decline teams in my system.

Keep in mind NE always outperforms their expected wins, and DET almost always underperforms theirs.

I think your Dolphins will be the Jets of '07 (a very-slightly above average team grabbing a wildcard thanks to a weak schedule).

Derek said...

Of course, I should give you credit again for the idea of using the system as a way of estimating season win totals.

I would imagine the Dolphins' schedule is tough, given that they're matched up with the AFC North and NFC East. I'll have to check your projections on next season's win totals again.

Brian Burke said...

I was thinking a neat idea would be to look at the expected win totals of "surprise" Super Bowl teams the year before their SB appearance. For example, the Ravens were 8-8 in 1999, but what was their expected record that year? I'd also look at the '98 Rams, '00 Patriots, etc. They may not have been that surprising at all, just unlucky the year before. I've got some time today, so maybe I'll crunch the numbers.

Brian Burke said...
This comment has been removed by the author.
Doug Walters said...

Hey you guys,

You know what's crazy? My system agrees for the most part with both of yours. Your lists of teams to improve and teams to decline almost mirrors mine, yet I use a completely different method of analysis.

Doug Walters said...

Brian

Check out the link below:

http://footballprofessor.blogspot.com/2007/05/pythagorean-estimates-and-actual.html

Your assumption that NE always outperforms their expected wins and vice-versa with Detroit is correct when looked at only in recent history. If you look at Pythagorean wins vs. actual results over a longer time period, you'll see that teams underperform their estimates when they're on a bearish trend (downward) and they outperform their estimates when they're on a bullish trend (upwards). Sure there are exceptional years when that's not true, but I think it happens enough to be considered "rule of thumb"

Derek said...

Doug, I've seen your blog and found the "macro"/systemic approach fascinating. Your rules of thumb, however, depress the Hell outta me as a Dolphins' fan, however. I wonder if the same is true of the AL/NL because the merged NFL has been around about a third as long, and three "epochs"/"eras" seems like a small sample.

Then again...
"They have a saying in Chicago. Once is happenstance. Twice is coincidence. Three times is enemy action."

Doug Walters said...

Thanks Derek, if you think the system scares a Dolphins fan just imagine how much it scares me (a Lions fan). From what I can tell there shouldn't even be a team in Detroit in about 5 years. Please God let the pain stop...