APBRmetrics

John Hollinger · Joined: 14 Feb 2005 Posts: 175

Not sure if everyone's seen this yet, but this is genius:

http://ballhype.com/story/the_foibles_of_formulas_a_quiz

KD · Joined: 30 Jan 2005 Posts: 163

NickS · Joined: 30 Dec 2004 Posts: 384

Everything Dan says is correct, but I want to highlight one portion for further comment

mtamada · Joined: 28 Jan 2005 Posts: 377

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

Harold Almonte · Joined: 04 Aug 2006 Posts: 616

Rebounding (DR/OR), like scoring (FGA=FGM/FGMissed) is treated as binary. That's what this possession logic says, and is true. But when you weight those stats, scoring has punishment between the stats, but rebounding not. In one "binary" mode, you are 1 or 0, in another you are +1 and -1, strange no?. But the most strange is that scoring can be -1 and -1, and the punishment must be done between FGMissed and DR.

But, the real problem is that the possibility of happening is not included. I don't know if this is a thing to be obviated when you weight. We are trying to include it at rebounding where as Dan said, there are almost infinite possibilities (but, the ranges of average are very narrow: near 70% after a FGMissed, lower than 60% after a block, and near 90% after a FTMissed), but I've never heard about using possibilities of happening at scoring. I would dare to bet this just would become scoring break even in the league average break even.

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

**Dan** **Rosenbaum** · Posted: Tue Dec 18, 2007 12:17 am Post subject:

GF:

Berri has complained that adjusted plus/minus is noisy, but that is a criticism I also have made. To be honest, I wish that Berri had criticized adjusted plus/minus more. My frustration is more due to his evasiveness and lack of substance in his responses to legitimate critiques of his model.

Yes, alpha could vary from team to team (just like our 0.44 free throws multiplier could vary from team to team), but Berri is assuming something very different. He is assuming that for every team it is zero on one side of the court and one on the other. That is a bizarre assumption.

**Dan** **Rosenbaum** · Posted: Tue Dec 18, 2007 12:25 am Post subject:

NickS:

Wins Produced is not assuming an alpha=0.5. Otherwise, the absolute value of the weights for rebounds and missed shots would be half that of the absolute value of the weights for turnovers and made shots.

NickS · Joined: 30 Dec 2004 Posts: 384

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

NickS · Joined: 30 Dec 2004 Posts: 384

To follow up, looking at this post the chart on page 103 of Wages of Wins (hardback) has the information I'm talking about.

You can find it by doing a "search inside this book" on amazon and searching for "opponent field goal".

All I'm saying is that there are entries on that chart that reflect value distributed at the team level, rather than credited to individual players, and that it helped me understand Wins Produced to think about how those fit into the model.

Think about the entries for "opponent's field goals made", "opponent's free throws made", and "opponent's turnovers" and what work they're doing. Think about why there's no line-item for "opponent's field goals missed".

I can just say that I came to this from trying to construct a scenario in which a losing team would have more Wins Produced than a winning team, and I found that those entries for "opponent's field goals made" etc were required to balance the values so that the team Wins Produced corresonded to the margin of victory.

Which then lead me to thinking about why, as I've said, a Field Goal Made is worth twice as much at the team level as a Defensive Rebound, but has the same credit given to the individual player. Phrasing it that way may be a tangent, but my point is that it also answers Dan's question about alpha.

Flint · Joined: 25 Mar 2007 Posts: 112

Berri responded to the Ballyhype column discussed above last night.

http://dberri.wordpress.com/2007/12/18/different-answers-same-conclusions/#more-674

NickS · Joined: 30 Dec 2004 Posts: 384

That's a great post by Berri, I agree with almost everything he says.

It also gets at my frustration with Berri, which is that he seems disinclined to talk about the choices that he's made with Wins Produced, it's strengths and weaknesses. He does talk about Wins Produced vs NBA efficiency and PER occasionally, but mostly as a way to talk about scoring efficiency, rather than engaging the model behind them (well, the model behind PER, I'm not sure there is a model behind NBA efficiency).

What's implied, in that post, is that Berri does understand the various other advanced statistics out there, it's just that, as a casual reader, he so rarely engages with them. Even more frustrating (from the point of view of this APBRMetrician, who likes to take models apart to see how they tick) Berri frequently describing the model behind Wins Produced as compelled by the regressions, rather than based on a combination of regressions and choices of model, as Dan points out in the opening post in this thread.

If Berri had more posts like that one, and engaged questions about the differencences in what is being measured by PER, PW%, Wins Produced, and adjusted +/- I would have far less complaints.