Saturday, January 09, 2010

How not to do statistics

Let me start by saying that i like The Painted Area blog. However, they have cooked up a stinky statistical stew that I suggest you do not eat:

We've found examining a team's rebounding margin is a quick, simple way of projecting playoff success....it was no surprise that strong rebounding is a key component to winning titles. But we found it interesting that out of the 40 teams to make the Finals in that 20-year span between '87 to '06, only four teams had a negative rebound margin for the regular season. We also found that the +1 rpg margin threshold seems to be a strong indicator if a team can win the title....Currently (stats as of 1/6/10), the Lakers (+2), Magic (+2.6), Cavs (+3.8) and Spurs (+4.1) are in good shape in the rebound margin department.

Ok, people got that? Rebound margin = playoff success and look, the best teams this year seemingly have a good margin.

Or do they?

Well folks, the league leaders in rebounding margin (as of 1/8/10) are the Memphis Grizzlies at 5.3. Interestingly the blog does not mention them as playoff contenders, but does mention the number 2 and 3 teams in the league which are the Spurs and the the Cavs. They also do not tell you that Portland and Chicago also have rebound margins higher than the LA Lakers.

Regarding the magic +1 margin as the cut off for greatness, there are 10 teams in the Association with such a mark and 6 of them are Memphis, Portland, Chicago, Detroit, Oklahoma City, and Utah. Will any of these teams win a playoff series this year? 

The other four are indeed Spurs, Cavs, Magic, and Lakers, but this test clearly has way too many false positives.



1 comment:

Trent said...

"Rebounding margin must die":

http://basketballprospectus.com/article.php?articleid=829