The Rebounding Myth

Posted on 11/23/2010 by

51



“Insanity: doing the same thing over and over again and expecting different results.”-Albert Einstein

I wrote in a private e-mail today:

Yesterday’s piece was one of those pieces that just happen. I’d been working all weekend on some consulting work I need to hand in and when I went to write the Around the Wow piece the quote “oh the places you’ll go” popped into my head. Before I knew it, I was looking up Dr. Seuss books.

For some reason, my spontaneous/unplanned stuff can be really good (the last 4 pieces were all like that), whereas some of the more thought out stuff leaves me unsatisfied. Weird.”

This is fortuitous because two days ago I wrote a post on the 100 worst seasons/players since 1978. This inspired some familiar responses.

Rebounding again?!?!?

The argument is diminishing returns for rebounding .

Now the studies referred have some technical problems ( If you run a regression you  must account for other variables that could affect your result). This is why you’ll see me control for small samples (minutes), age, position and teams frequently. Prof. Berri’s covered this before in the comments here http://dberri.wordpress.com/2010/05/01/ted-leonsis-endorses-stumbling-on-win or very thouroghly in Stumbling on Wins just buy the book). I’ve covered this before (see The Basics , and here ).

In the book (which I recommend you buy :-)), the finding is that there is diminishing returns with respect to defensive rebound but not for  for offensive rebounds. The overall  though the effect is quite small.
But the Zombie argument remains unabated and it goes like this:
1. Rebounds dominate Wins Produced
2. Diminishing Returns dominate Rebounds
Therefore Wins Produced as a model is skewed and significantly overrates/underrates players.

I tried a GIS for Zombie Troy Murphy but nothing came up (Image courtesy of xkcd.com)

If this were a true statement then season to season fluctuation in Wins Produced would have to be huge and would make predicting the season a ridiculous exercersize (seriously, read any piece on this blog) and rebounding numbers would fluctuate wildly from season to season.
As I said, I cover point one all the time and for the purposes of this discussion (and posterity) I’m going to cover point Number 2. Here’s how:

I pulled every players rebounding numbers from 1979 on (for every player with > 800 minutes played, see controls).
I looked at every player’s:

  • offensive rebounds per 48 minutes (orb48)
  • defensive rebounds per 48 minutes (drb48)
  • total rebounds per 48 minutes (trb48)
  • And for Grins and giggles, looked at all players and a subset of player ages 25-30 (see more controls, this time for age).

For your amusement that table is here. (This also allows for peer review of my findings).

My results? Here:

Do rebounding numbers fluctuate wildly based on teammates and diminishing returns? Short answer is no.  Year to year correlation for total rebounds per 48 minutes is at 91% regardless of the age grouping. In fact, 82% of the population in the sample had an absolute error in year to year rebounding of less than 1.5 rebounds. If I break out the Minitab as well and graph it up:

And that looks like the very definition of a normal distribution.

So Wins Produced consistent season to season? Check

Rebounds not varying radically? Check

Unnamed individuals pestered into writing additional material on this? Check and check (You’ll just have to wait to find out).

Scott Meyer needs to get out of my head!!!

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