APBRmetrics

DSMok1 · Posted: Wed Feb 09, 2011 8:57 am Post subject:

I think it will be possible to apply aging curves, back2newbelf, as part of a pre-processing phase. Once that is done, I will be interested in what length of time is best...

Aging curves in preprocessing: for each player, convert his value in the past to current value. If the player was 21 in the previous matchup and now is 25, take the aging from 21 to 25 and add it to the observed score in the previous matchup. Probably just do this at a yearly basis; I have a rough aging curve for APM calculated that I use for ASPM. After the preprocessing, do the same calcs you just; I expect to see maybe even the 5.x take over the best position, and the overall error be significantly lower (maybe the lambdas lower as well).
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**Ilardi** · Joined: 15 May 2008 Posts: 265 Location: Lawrence, KS

back2newbelf,

A couple quick questions:

1) did you include playoff data in your models?
2a) did you weight each season equally?
2b) if so, have you explored the effect of differential weighting across seasons?

back2newbelf · Joined: 21 Jun 2005 Posts: 275

EvanZ · Joined: 22 Nov 2010 Posts: 298

b2nb, question...

Is it possible to break out the rebounding component of the offensive and defensive RAPM?

The reason I ask is because I'm doing some validation of ezPM. One of the things I want to do is regress each individual component of ezPM (off100, def100, reb100) against the components of RAPM, if possible.

As a test of ezPM (and maybe a suggestion for you to do with RAPM), I have regressed ezPM100 against each of its internal components (O100, D100, REB100). Here's the summary for the REB100 regression:

back2newbelf · Joined: 21 Jun 2005 Posts: 275

updated this seasons' ranking http://stats-for-the-nba.appspot.com/ranking11
I still recommend the 4 year ranking though

By 1 year appr RAPM:
-Udoh is now the top rookie, the Warriors are +3.2 when he plays, -4.3 when he doesn't. Wall looks atrocious
- two 'no names' in the top 20: Keyon Dooling and Anthony Tolliver

A whole bunch of Bulls players are rated as above average defenders. I think it's all coaching
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greyberger · Joined: 27 Sep 2010 Posts: 52

On the subject of APM, Arturo Galletti has a post about the APM available at basketballvalue.com.

I didn't know that a SPM-type regression was involved until I read the details. That would seem to be a key point of distinction between APM there and hypothetical public alternatives. Are there any good posts or links about this step in the Rosenbaum approach? I'm not even sure I'm asking the right question.

How about this one: any responses provoked by the Arturo post?

DLew · Joined: 13 Nov 2006 Posts: 224

Arturo clearly got a little confused there... Adjusted plus-minus is not easy to understand, especially for people who come in with a prior belief that it's not a good method. If Arturo actually wanted to understand APM you would think he would post in this forum or check out Eli's very informative work on the topic.

greyberger · Joined: 27 Sep 2010 Posts: 52

In the post he says he's been working on this for 'months' (before 'breaking out his pimp hand') Rolling Eyes

Just to be clear and to satisfy my special curiosity:

Adjusted +/- at BValue.com does not use a SPM component as AG claims?

bchaikin · Joined: 27 Jan 2005 Posts: 690 Location: cleveland, ohio

wait a minute...

you claimed in a previous thread:

Adjusted plus-minus... when compared to all other overall player rating systems... is clearly superior when done properly.

when questioned with some spurious results of adjusted plus minus, and whether you could substantiate them, you blew off that questioning with:

No, I have contractual obligations not to, and frankly I wouldn't care to if I was allowed. If you choose to make an effort to understand adjusted plus-minus then you'll likely come around, but I suspect you've already made up your mind about it.

but now when someone actually does make the effort to understand the process, you respond with:

Arturo clearly got a little confused there... Adjusted plus-minus is not easy to understand, especially for people who come in with a prior belief that it's not a good method. If Arturo actually wanted to understand APM you would think he would post in this forum or check out Eli's very informative work on the topic.

now you are blowing off the attempt to understand it with the caveat that they say it doesn't work because they don't want it to work and must have some grudge against it...

on the one hand you are saying people need to make an effort to understand the process, but when they actually do you say it's not easy to understand...

i read through his posting - several times - including the comments section. and my question for you is this - how do you respond to his statements?

Calculating Adjusted +/-

The final step is to take the Pure regression and the Stats model and adds them up by player like so:
APM = x* Pure +/- + (1-x)*Statistical +/-

And proceed to adjust x between 10% and 90% for each player to minimize the error. In essence he tweaks the rating to get a high R-Square. To summarize, the APM model calculates two variables with a low correlation to wins (R^2 <5%) and adds them up to minimize the error and guarantee a 90%+ Rsq. for the overall model.

Funny that.

What does this mean exactly? Well, the R^2 for the APM model is very much a fabrication. The correlation to point margin & wins of the model shown in Basketball value is artificially inflated by adding the error back in.

that last line is a pretty serious claim. if what he is saying is true, that the players values (normalized to player minutes played) do not add up to team wins (or team average per game point differential) without a fudge factor, then the value of the process for player evaluation is severely weakened...

i am not saying he is correct, but am simply asking - how do you respond to that?

greyberger · Joined: 27 Sep 2010 Posts: 52

Apparently this is much ado about nothing. Arturo is commenting on a SPM technique outlined in a 2004 Rosenbaum piece. He incorrectly describes this as being the foundation for BV.com's APM ratings.

Apologies for hijacking the thread.

back2newbelf · Joined: 21 Jun 2005 Posts: 275

DLew · Joined: 13 Nov 2006 Posts: 224

Bob, I think greyberger's comment pretty much summed things up...

Crow · Joined: 20 Jan 2009 Posts: 822

Looking again at back2newbelf's Coaching only Adjusted +/= for the most recent 5 years I found a few trends:

Only Scott Brooks was +1 or better on both the offensive and defensive splits. Aided by the favorable comparison to the previous stretch with PJ Carlesimo.

Of the top 10 actives, 6 are in the east, 4 in the west.

Of the bottom 17 out the total of 67 Coaches active during the time period only 2 are still active. Only three Coaches -1 or worse overall are active.

There were 10 Coaches estimated to have more than a 2 point helpful impact on defense. No Coach was +2 on offense. 2 active coaches are over +1.5.

Only 6 of the 67 were over +1 on offense. 13 were estimated to have more than a 1 point helpful impact on defense. 20 were estimated to have more than a 0.5 point helpful impact on defense. 14 on offense. Only 3 better than 0.5 positive impact on both, so except for those rare occasions the better Coaches are estimated to be notably helpful on just one side of the court.

15 were estimated -1 or worse on offense. 13 on defense. None on both.

back2newbelf · Joined: 21 Jun 2005 Posts: 275

Some of this stuff appeared here http://www.slate.com/id/2287339/
But I have to say, if that's the way magazines write about my work I don't want my stuff to appear anywhere.
Writing about a certain technique, then saying that it might actually a bad technique because one person said so and cite the critique, while failing to realize that (1) the person who wrote the critique only has comments on the original model and (2) that it has been proven that using ridge regression instead greatly improves performance.. that's just beautiful.

no wait, that's bad journalism
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