NBA teams win 7 games more when their coach is a former All-Star
I'm shocked by the results of this NBA study: "Why Do Leaders Matter? The Role of Expert Knowledge." It's by Amanda H. Goodall, Lawrence M. Kahn, and Andrew J. Oswald.
Basically, the study tries to figure out if having been a successful NBA player would make you a more successful coach. The answer: yes, and hugely.
After controlling for a bunch of possible confounding variables, it turns out that:
-- for every year the coach played in the NBA, his team will win an extra 0.7 games per season [over a coach who never played].
-- if the coach was *ever* an NBA All-Star, his team will win an extra 7 games per season.
That last number is not a misprint. I'll repeat it in bold:
A coach who was an NBA All-Star at least once is associated with a 7-game increase in team wins.
The result is statistically significant, at 2.5 SDs above zero.
What could be causing this?
My first reaction was that teams who spend a lot of money on talent might also willing to spend to hire a high-profile coach. But the study controlled for team payroll, so that can't be it.
So what is it? I can't figure it out, but I'd bet a lot of money that it's not (as the study thinks it is) that All-Star coaches are somehow "experts" in getting the most out of their teams. I see no reason why it should be assumed that better players would make better coaches (and, in fact, I have heard plausible arguments the other way, that guys with natural talent have no idea how they do it, and so can't teach others to do the same).
For the record, here are the other variables controlled for: payroll, race of coach, age and age squared, NBA head coaching experience (and experience squared), college head coaching experience, "other pro" head coaching experience, and number of years as an NBA assistant coach.
(In the study, I am looking at the regression with no team fixed effects. That's Table 1, bottom panel, second from the right. There were 16 All-Star coaches in the sample, for 68 seasons. The authors don't list them.)
Any ideas? I feel like I must be missing something ... coaches can't be contributing seven wins to their team just because they were better players. Could they?
(Hat tip: Andrew Leigh via Justin Wolfers.)