APBRmetrics

Mountain · Joined: 13 Mar 2007 Posts: 1527

If pure +/- is the main solution I think it will be pure +/- with an array of many splits and parts.

As I've noted before Dan Rosenbaum introduced pure +/- and then seemed to immediately move to "overall +/-" with his statistical as about an 80% and pure at just 20%. I would really appreciate hearing from any the next pure adjusted stat producers if they considered following with a blended product or why they choose not to.

And at this time I am no longer a fan of a 80% statistical 20% pure split because I tend to think this ends up shorting defense again.

I wonder if something like 60% statistical / 40% pure or 50-70% statistical on offense depending on usage and therefore 30-50% pure offensive adjusted and maybe 40-50% statistical on defense and 50-60% pure defensive adjusted would be "better". A fuller blend feels more promising to me.

Ilardi · Joined: 15 May 2008 Posts: 265 Location: Lawrence, KS

Ilardi · Joined: 15 May 2008 Posts: 265 Location: Lawrence, KS

gabefarkas · Joined: 31 Dec 2004 Posts: 1313 Location: Durham, NC

gabefarkas · Joined: 31 Dec 2004 Posts: 1313 Location: Durham, NC

Ilardi · Joined: 15 May 2008 Posts: 265 Location: Lawrence, KS

Ilardi · Joined: 15 May 2008 Posts: 265 Location: Lawrence, KS

schtevie · Joined: 18 Apr 2005 Posts: 409

I think Gabe's in a mood.

What must be the case is that the counterpart positions on 82games are defined by offensive designation. No doubt that CP was the offensive point guard 100% of the time.

Mountain · Joined: 13 Mar 2007 Posts: 1527

Alright Steve. Thanks again for the thoughtful replies.

gabefarkas · Joined: 31 Dec 2004 Posts: 1313 Location: Durham, NC

schtevie · Joined: 18 Apr 2005 Posts: 409

Gabe,

I did not recently accuse Bob of "splitting hairs and twisting around conclusions". In fact I didn't say anything on the matter. OK, I thought about it, but I didn't.

The fact remains that there is an interesting contrast between general perceptions of CP's defensive abilities and what APM says. It is an anomaly worth discussing. One factor explaining the gap might be the one I described. The numbers will be crunched at Steve's convenience and the relevance of the resulting estimates may or may not be confirmed by someone who could say whether in fact CP did in fact spend his time guarding 2s.

Regarding APM generally, who says it is a panacea? Is there a better single metric, in concept, that is its superior? No, and by definition there cannot be. Underline it. Can the metric be improved by including age profiles, position adjustments, etc. Absolutely, and that is the (hopefully near-term) future.

Finally, I don't understand your objection to dividing APM into Offensive and Defensive components. I just don't.

gabefarkas · Joined: 31 Dec 2004 Posts: 1313 Location: Durham, NC

I appreciate your candor. If it appears our positions are intractable, as you describe, and you just don't understand my objection, then let's put this matter to rest. For the record, I'm not an opponent of APM. I'm just in general a skeptic.

bchaikin · Joined: 27 Jan 2005 Posts: 687 Location: cleveland, ohio

The fact remains that there is an interesting contrast between general perceptions of CP's defensive abilities and what APM says. It is an anomaly worth discussing.

not sure where the anomaly exists. you have a person who watched hornets games (in 07-08 ) tell us this about chris paul:

I really don't understand all of this statistical stuff,but as someone who has actually watched most of the Hornets games I'm somewhat confused by the repeated claim that Jannero Pargo is a good defender or a better defender than Paul. Pargo is probably one of the worst defenders in the NBA and as a player he's utterly useless when his shot isn't falling.

In fact I'm relatively sure that a lot of this discussion is a result of conflating Pargo's defense with Paul's. Before Pargo got hot and began to actually contribute I looked at 82games.com and Paul's defensive PER was around 14.5 or something. His differential PER was in the top five in the NBA because he was producing at better than twice the rate of opposing PG's. At that point Pargo was basically his backup and the Hornets hadn't yet given up on Morris Peterson. After Pargo began to produce he took much of Peterson's minutes,Pargo and Paul would probably play around 15 to 20 minutes per night together. Paul always guarded the stronger player because Pargo is completely incapable of dealing with larger players. That is to say that Pargo nearly always guarded the opposing point guard. Immediately Paul's defensive PER began to skyrocket.If you watched the games you'd see that teams go right at Pargo at every opportunity and that he offers very little resistance.

and a person who charted hornets games tell us this about chris paul:

Here are some numbers; The guy he was guarding scored .87 points per offensive action, (on 1203 actions). The best number on his team was .80 held by Rasual Butler (313 actions). Pargo's numbers were 1.01 on 620 actions.

The numbers I gave were for 07-08. His defensive numbers for 07-08 were above average for the PG position, his numbers for this year are also above average for the PG position.

and the people that quite possibly saw him play the most (coaches/sportswriters) vote him onto the all-D 2nd team and 2nd overall in MVP voting...

but another person who neither watches chris paul ("extensively") nor charts hornets games tell us this:

virtually everybody has trouble believing that a guy with eye-popping boxscore stats and horrific defense is really as big a liability as adjusted plus-minus says he is (think: Al Jefferson, Carmelo Anthony, CP3, etc.)...

that's why adjusted plus-minus is so potentially valuable - by unmasking the fact that players like Calderon and Carmelo and Al Jefferson and Richard Jefferson and Amare Stoudemire don't have nearly the positive impact that people think they do, because they give away on defense much of what they add on offense (if not more, in some cases).

Although Chris Paul was one of the Top 3 offensive players in the league (+9.24), he was actually a liability on the defensive side of the ball (-4.54). As a result, his overall contribution (+4.69), while impressive, was not commensurate with that of a top MVP candidate.

yet later tries to modify his comments:

In the thread on CP3's defense last year... I still concluded that he was a liability on defense in 07-08... but not to the extent that this completely "negated" his off-the-charts offensive contributions.

it would be a mistake to look at a player's defensive APM number from a given season and conclude: this is a valid rating of Player X's defensive ability. Rather, it's merely an indicator of his defensive contribution over the period in question

even if this interaction effect is found to account for much of CP3's improvement on defensive APM this year, it would not fundamentally call into question the validity of the APM approach to player evaluation.

if anything the anomaly is the methodology, which i believe we all want to work...

but when claims like the above are made, or:

http://blogs.wsj.com/numbersguy/mark-cubans-surprising-player-performance-numbers-580/

that "...sebastien telfair is more valuable than dirk nowitzki...", i can see why some may be skeptical or why someone might say adjusted +/- is "...one of the most overhyped player rating systems..."...

schtevie · Joined: 18 Apr 2005 Posts: 409

Bob. To my surprise, I find that to be a rather reasonable summary of the discussion. I look forward to seeing what additional numbers Steve comes up with regarding interaction effects.

As for APM being "...one of the most overhyped player rating systems..." however, I don't follow. First, I don't see much hype. Second, if you share this view, then you are at least implicitly of the belief that, overall, APM has shortcomings relative to another rating system. Is this true, or does your dissatisfaction relate only to particular estimates, such as CP's defensive APM in '07-'08 that don't pass your laugh test?

deepak · Joined: 26 Apr 2006 Posts: 665