[82games] Adjusted +/- Ratings for Rockets

82games has published a new article on adjusted +/- (a metric that attempts to capture what Daryl Morey referred to as "ground truth" some time back [source]).

http://82games.com/ilardi2.htm

This stuff is interesting to me, though I expect many of you will think its boring and/or useless. Anyways, here's some introductory text in the article explaining the idea for those who aren't familiar with it:

[rquoter]
Like most devoted NBA fans, we enjoy looking at boxscores. They’re often incredibly informative. And yet boxscores fail to capture many important elements of play – lockdown defense, screens, rotations, hustle plays, and so on – that can affect the game’s bottom line.

That’s why we believe it’s necessary to “think outside the boxscore” in order to adequately measure each player’s true value to his team. The plus-minus statistic, which tracks all changes in scoring while each player is on the court, is one promising approach that’s gained traction in recent years. But this metric suffers from a key drawback: each player’s rating is heavily dependent upon the quality of his on-court teammates. Even a mere role player on a great team (e.g., Glen Davis) typically has a higher plus-minus rating than a superstar on a bad team (Dwyane Wade). Fortunately, this limitation can be overcome through the use of advanced mathematical techniques, which make it possible to isolate the unique effects of each player on the court. In other words, we can statistically adjust each player’s plus-minus rating to account for the simultaneous impact of all his teammates and opponents [1]. Hence the name: adjusted plus-minus [2].

At first blush, the metric might even seem like the “holy grail” of basketball statistics – a single measure that captures the precise effect of each player on his team’s bottom-line scoring margin. But it, too, has a major drawback: as a mathematical estimate, each adjusted plus-minus rating contains measurement noise, i.e., a margin of error.

It’s important, therefore, to get this noise (error) level as low as possible, and we’ve taken an important step in that direction with the present set of ratings. Specifically, we’ve used five seasons’ worth of data (provided by 82games.com) – weighted very heavily in favor of the 2007-2008 season – to disentangle the individual effects of teammates who frequently appear on the court at the same time. As a result, we are able to present below the most accurate (low-noise) adjusted plus-minus ratings ever to appear in the public domain. In addition, we’ve modeled separately each player’s impact on offense and defense, treating these as completely independent variables. (Both innovations are explained in detail below the fold.)
[/rquoter]

Here are ratings for the 8 Rockets players to have played multiple seasons (probably more reliable than the numbers for our 1-year players):

Code:

[B]player              Off         Def        Total[/B]
Yao Ming           +0.21       +4.56      +4.77
Tracy McGrady      +4.89       -2.05      +2.85
Ron Artest         +1.79       +4.52      +6.31
Rafer Alston       -0.51       -0.46      -0.97
Shane Battier      +0.87       +1.83      +2.69
Chuck Hayes        -4.22       +9.76      +5.55
Luther Head        -0.37       +0.60      +0.23	
Brent Barry        +2.11       -2.53      -0.41

Just for fun, I plotted the Offense and Defense +/- from above to make it easier to visualize:



I thought it was interesting how these results fit into my intuition for how these players help on both sides, without relying directly on the boxscore stats. Ron's a great 2-way player, and that's confirmed here. T-Mac and Brent Barry are both good offensive players who can be liabilities on the defensive end (for different reasons), and that shows here. I added a red box in this plot which represents lower and upper bound for players falling in the 40%-60% percentile in offensive +/- and defensive +/- for all current players who've played at least 2000 minutes last year. That's a long, possibly confusing sentence -- I hope you get the meaning. I was somewhat surprised that this rating is much more favorable towards Yao's defense than offense. Though I have felt that with Yao in the game our offense tends to be more turnover-prone, and there is typically less fast breaking opportunities. Maybe that's what's going on there.


Please also take note of the errors in the link above; their method was designed to reduce the error as much as possible, but it's still a noisy stat.

Here are some particular observations the article making about the Rockets. They like our team:

[rquoter]
Because of his defensive prowess (+4.52), Ron Artest was rated as one of the top 20 players in the league last year. Historically, Houston has obtained many players whose impressive adjusted plus-minus ratings belie their less-heralded reputations: Artest (+6.31), Carl Landry (+6.55), Chuck Hayes (+5.55), and Shane Battier (+2.69). If Yao Ming (+4.77) and McGrady (+2.85) remain reasonably healthy this year, the Rockets may be regarded as the leading contenders to emerge from the West.
[/rquoter]

 

Yeah, I just edited my post to kind of address that. That is interesting, to say the least. Though, last year I thought we struggled a bit incorporating Yao's strengths into Adelman's offense.

And as I wrote above: I have felt that with Yao in the game our offense tends to be more turnover-prone, and there is typically less fast breaking opportunities. Maybe that's what's going on there.

 

I don't think you can take the ratings that literally. They may help for very general impressions. Parker has a +0.67 with a +1.3 error. That's not very conclusive, one way or the other. He apparently doesn't have a great impact on the team's offense like some stars, but he isn't necessarily "below average" either.

Yeah, that's pretty strange also.

 

But remember, the adjusted +/- takes into account everyone on the floor -- teammates and opponents.