Monday, November 16, 2009

Balance in the NFL Going to Sh*t?

Over the past few weeks (and especially after the beatdown that New England laid upon the Titans) I've been hearing commentators, colleagues, and friends claim the NFL just isn't very interesting this year. The claim is that the competitive balance of the league, or the evenness between the teams, has taken a huge downturn and there must be something wrong with the league's construction. My first thought is that the NFL has long been generally thought of as the most balanced league of North America's Big 4 and any change it would see would most likely be downward (when you're at a peak, the only way to go is down). My second thought was that, yes, there do seem to be a large number of blowouts this season. But looking at the standings, I just don't see that clearly. There are only 4 teams with more than 6 wins thus far in the season, and yesterday the awful Redskins beat the not-so-long-ago-unbeaten Denver Broncos.

Now that we're at a point where everyone has played 9 games (except for the Browns and Ravens tonight, but for the sake of saying this year is unbalanced, I'm assuming the Ravens win) I decided I'd check to see if there has been a significant change in balance this season. I'll just use a simple Ratio of Standard Deviations (RSD--a measure popularized by Roger Noll and Gerald Scully). This measure is a ratio of the standard deviation of winning percentages (SD) divided by the "idealized" standard deviation in a perfectly balanced league (ISD). A perfectly balanced league is defined (as all teams having a record of 0.500)--this is a stupid mistake on my part as noted in the addendum below...especially since I work with this data a lot. The reason for the denominator is to control for the number of teams and number of games played in each season to make it comparable across sports or seasons in which these variables change. The lower the RSD, the better the balance. From 2001 to 2008, the RSD was as follows:

2001: 1.628
2002: 1.321
2003: 1.535
2004: 1.540
2005: 1.694
2006: 1.447
2007: 1.661
2008: 1.658

And at the 9-game point in the 2009 season, we see: 1.448

So, at this point in the season, it looks as though we're on the better end of the balance spectrum (if you believe that more balanced means a better league--which, of course, is always up for debate). Keep in mind that RSD is not the only way to measure balance. However, it works as an interesting quick check on the distribution of wins around the league. It very well could be that there is a huge gap in talent between the top and bottom teams, where the best teams pummel the worst. We've seen some of this, but we've also seen the Redskins beat the Broncos and the Raiders beat the Eagles.

To be honest, I enjoy a demolition every now and then. Watching the spectacle of Tom Brady throwing 6 TD passes in one quarter is a lot of fun for me. It would probably get boring if there weren't teams that could challenge the Pats, Colts and Saints, but I don't think there's any lack of competition in the NFL as the Saints last few games have shown. I'm not ready to conclude that the NFL system is now completely broken, so let's not rush to fix it.

ADDENDUM: Guy points out a problem with my explanation. The ideal league isn't one with all .500 teams, but one where each team has a 50% chance of beating any other team. He makes some points about the difficulty at the extremes for balance, which are good to keep in mind. The correction for the model in terms of season length can overcorrect for short seasons like 9 games, making the RSD look more balanced than the league actually is. Given this, I still don't think balance is a hugely significant problem in the NFL this season as some commentators have tried to point out.


Thanks to http://www.rodneyfort.com/ for the data on past NFL season RSD. You can find the data for this post, as well as numerous other sports business data files by clicking the link on the sidebar.

4 comments:

  1. Millsy: The RSD does not properly correct for season length. As a result, RSD can give you very misleading results. For example, the NFL is historically one of the LEAST competitive of the North American sports, roughly tied with the NBA and much less competitive than baseball (though recently the NBA has been a bit less competitive).

    RSD overcorrects for short seasons. That's why you appear to see an improvement over 9 games. In fact, if the current spread in true talent in the league continues, you will see an RSD of about 1.72 at the end of the season, making it the least competitive season of the decade (though only by a little).

    And one small correction: a perfectly balanced league is not a team where every team is .500, but where all teams have equal talent (i.e. an equal .50 chance of winning against all opponents).

    ReplyDelete
  2. Thanks for the comments, Guy. I've been curious about the full correction myself when it comes to this point in the season and I agree the metric isn't perfect. I'm still not ready to say balance is out of whack in the NFL this year.

    You do point out a pertinent problem in my explanation of the metric. You are correct that it's all teams have an equal chance of winning each game.

    ReplyDelete
  3. Sure, things could easily tighten up over the last 7 games. However, if you go back and calculate the SD of win% at the 9-game mark of past seasons -- which may not be worth the trouble -- I think you'll find they were a bit smaller (i.e. more competitive).

    Actually, looking at teams' point differentials would probably be more accurate at this point (since W-L records include some additional noise due to luck). Let's check......
    Yes, there's been a pretty big increase in the SD of point differential per game: 6.7 in 2008 and 8.5 now. My guess is competitiveness is down a bit (whether too much is a matter of opinion) -- at least that's what the limited evidence we have suggests.

    Do most sports economists actually believe that the NFL is highly competitive, based on the RSD analysis? I find that extraordinary....

    ReplyDelete
  4. I personally think NFL is a fairly balanced league. However, I also feel that I misspoke in my post. I think the idea I wanted to convey was that most people view it this way (as in the general public). I can't speak for anyone else...especially in an economics profession. I think in a 16 game season there is a significant amount of noise, so it's really hard to tell. RSD can help, but like I said, and you confirmed even more so, it's not a perfect measure.

    I was actually hoping to go back and look at the scores. Thanks for the addition. As I said in my post, I think there could be something to the vast difference there seems to be between the top and bottom teams when they play one another. But I do think the middle of the road teams are pretty even. I don't think there's too much cause for alarm.

    With that said, I think a metric that may be useful in the analysis is Tail Likelihood. I've had trouble finding a full description of how it's actually calculated or to really get to the core of what it tells us. I find this unfortunate. In general, it gives us more information about the extremes, but I can't comment much further.

    I've got a busy week ahead, but had hoped to take another look at this topic as well. Perhaps by next weekend I can get a little more data out there.

    ReplyDelete