Talking Coaches Again
To quote Prof. Berri’s last post on the subject:
Readers of Stumbling on Wins would note that Bradbury’s results for baseball are quite similar to what we reported for the NBA. The study we review (which I co-authored with Mike Leeds, Eva Marikova Leeds, and Mike Mondello and published in the International Journal of Sport Finance) looked at 62 NBA coaches across thirty years of data. Across this sample, only 14 coaches were found to have a statistically significant and positive impact on player performance. So most NBA coaches – like most baseball managers — do not appear to make their players more productive.
We, as NBA fans, may hear a lot of noise about what a difference a great coach can make. I can even list some of the more commonly repeated refrains :
- He’s a leader.
- He’s a motivator.
- He inspires his team.
- He makes his team better.
But as Dave notes, this is not – for the most part – generally true. The simple truth is that NBA coaches are overvalued. Players are who they are and coaches don’t generally affect that.
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Given this glaring fact, how then can we objectively rate coaches? Is there any actual value in the function of coaching – and if there is, how do we capture it? I’ve struggled with these questions for some time**. As with most things in my life, the answer came to me in the form of a graph.
Not quite like this (Image courtesy of xkcd.com)
Coaches matter because they decide who plays
The graph in question contains every player season since 1978 for the National Basketball Association (all 14698 of them). Each point represents a player playing for one team for one season and shows their minutes played per game and their Wins Produced per 48 minutes played. It looks like so:
In essence this is a graph of a player’s perceived value in the eyes of their coach (as represented by the minutes played per game) and their actual value (as represented by their actual productivity in WP48). The thing that jumps out very quickly is that while there is correlation between perceived and real value (see the R2 = 32%) that only accounts for 32% of the variation we see.
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Did I lose you? Let me break it down for you. A player’s actual playing ability only accounts for less than a third of the variation we see in playing. What that means is that every time you scream at the television that the wrong guys are getting the playing time, there’s a good chance you are correct.
It hasn’t gotten better over time either.
This of course led me to a deeper examination of the data. What I found is that there are real differences on a year to year, team to team basis in that value versus playing time correlation. Teams and coaches simply do not play their best players; instead they play the players who they think are their best players.
That makes all the difference in the world.
So coaches do matter, but not in the ways that the media tries to sell us. It’s not about what book Phil gave Ron or the relationship Larry has with Allen. It’s not about the respect everyone has for Pop. It’s about who they put on the court.
Coaches control the minutes and everyone knows this. The surprising thing is that proper allocation of those minutes is actually a rare skill.
The 2011 Coach of the Year: Doug Collins
Let’s take a look at how well NBA coaches did this season in terms of playing their best players. Which coaches should be rallying the troops when it really matters?
The highest correlation between talent and playing time was enjoyed by Doug Collins and the Philadelphia 76ers. By the numbers, Doug Collins got more out of his roster than any coach in the league – by a wide margin – and was thus an easy choice for 2011 Coach of the Year. A coaching top five of Collins, Thibodeau, Popovich, Spoelstra and Hollins is not bad. The bottom of that list doesn’t hold many surprises either.
Before anyone complains that Phil Jackson is left on the outside looking in, I’ll just say that historically he does very well. We’ll get to that in part 2!
Arturo Galletti is the Co-editor and Director of Analytics for the Wages of Wins Network. He is an Electrical Engineer with General Electric in the lovely isle of Puerto Rico, where he keeps his production lines running by day and night (and weekends) and works on sport analysis with his free time.
**Editor’s Note: Arturo has actually wrestled with this issue before. Check the links below if you’re interested