Theodore Vasiloudis writes:
I’d like to bring your attention to this article by Benjamin Morris discussing the value of steals for the NBA. The author argues that a steal should be a highly sought after statistic as it equates to higher chances of victory and is very hard to replace when a player is injured.
I would argue that the reason behind the correlations showing this data is the fact that steals are much more rare in an NBA game than any of the other stats examined so their contribution is exaggerated.
I looked at Morris’s article and it looks like he’s running a regression of players’ plus-minus statistics on points, rebounds, assists, blocks, steals and turnovers. He writes, “A marginal steal is weighted nine times more heavily when predicting a player’s impact than a marginal point. For example, a player who averages 16 points and two steals per game is predicted (assuming all else is equal) to have a similar impact on his team’s success as one who averages 25 points but only one steal. If these players were on different teams and were both injured at the same time, we would expect their teams to have similar decreases in performance (on average).”
I’m not quite sure what is being done, though, because plus-minus statistics have been well known for awhile (see here, for example, from 2007) but Morris does not use the term “plus-minus” nor does he connect to the literature on it, instead writing, “I [Morris] used this technique quite a bit throughout my treatise on Dennis Rodman, though it is actually better suited to broader analysis such as this.” So this suggests to me that, either I’m missing something or Morris is. I expect I’m the one who’s out of the loop here, so maybe some of you readers can help out.
From a statistical point of view, we have the usual challenge of distinguishing correlation from causation. I don’t think Morris is literally saying that the marginal benefit of a steal is 9 points. To calibrate, one might try to figure out the marginal benefit of a 2-point shot, which I’d think would be on average a bit less than 2 points because of the possibility of an offensive rebound. Or, for that matter, the marginal benefit of a rebound. But, for Morris’s goal of player evaluation, the causal effect is not what’s important. Rather, his finding is that teams have a better point differential when players with more steals are in the game. This seems like a reasonable enough regression to me, but at the same time I agree with Vasiloudis that the conclusions look odd. There’s not enough of a trail of bread crumbs for me to have confidence in the result. Which is not to say that I think it’s wrong, I just don’t quite know what to think of it.
P.S. Lots of good stuff from commenters who know a lot more about basketball than I do.