Thursday, May 07, 2009

USA Today's NBA salary data is flawed

My previous post pointed to a blog entry by sports economist Stacey Brook, in which Brook found a low correlation between team payroll and wins. Specifically, he found that for the 30 teams in the 2008-09 NBA, the r-squared was only .0410.

I think Brook used incorrect data. The article he pointed to in turn poined to the USA Today basketball salary page. However, the USA Today database misallocates salaries. When a player was with more than one team in 2008-09, it counts his entire salary for only one of those teams. That throws everything off.

For instance, mid-season, the Raptors traded Jermaine O'Neal and Jamario Moon to the Heat for Marcus Banks and Shawn Marion. All four of those players are listed on the Raptors page. This (and probably other similar situations) causes the Raptors payroll to come out to $95.3 million, compared to only $67.4 million at other sources (like this one). And since all four of those players are absent from the Heat page, Miami comes out with a payroll of only $50 million instead of $68.6 million.

If you use the more standard numbers, you wind up with a solid positive relationship between salary and wins, an r-squared of .2561 instead of .0410. (That's an r of .5061.)

This doesn't affect any of the comments I made in the last post (or plan to make in future posts), but I thought I should report it anyway.

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At Tuesday, July 14, 2009 5:47:00 PM, Blogger Darren said...

Hey Phil,

Interesting post. I'm currently trying to source data for a small student project on the NBA contract year. Have any suggestions?

I'm glad I read this. As at this point, I haven't taken those things into consideration.


At Tuesday, July 14, 2009 6:26:00 PM, Blogger Phil Birnbaum said...

Hi, Darren,

Hmmm ... nope, don't know of any NBA contract data offhand. I'd try ... if that doesn't work, I'd ask on the APBRmetrics boards.

Maybe someone reading has a suggestion ...


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