By Henry Johnson
Earlier this week, we used data from Basketball-Reference to examine the NBA’s trend toward older coaches. Now, let’s look at whether coaches of different ages see different outcomes. To do this, we can create a model that predicts the winning percentage of a given team based on its coach’s age. The results of this model are as follows:
Coach age is correlated with winning percentage in a way that is almost significant at the 0.05 level. Because the estimated coefficient is positive, the model tells us that older coaches fare better and that a one-year increase in coach age is associated with a 0.09% increase in winning percentage. Given the model’s low R2 of 0.002, coach age is not a terribly informative piece of data, but the relationship is almost significant nonetheless.
There is, however, a major flaw in the model: survivorship bias. Old coaches who are bad are harder to come by because they’re typically fired before they can get old. As a result, the older NBA coaches who are left are disproportionately successful. For this reason, we should control for years of experience. When we do so, our model yields the following results:
Suddenly, we get a different story. Once you control for years of experience (which is a strong predictor of performance), the coefficient on coach age is actually negative. This relationship is significant, and it suggests that younger coaches fare better. Accounting for years of experience, each one-year increase in coach age is associated with a 0.135% decrease in winning percentage.
The optimal coaching candidate for NBA teams is someone with a blend of youth and experience. This model says that we’d expect the most successful coach in the NBA to be Doc Rivers, not exactly a kid at age 55, but who has amassed 17 years of experience in a relatively short amount of time.
Looking only at coaches in their first year—a subset that excludes successful, long-tenured coaches like Gregg Popovich—experience is still a significantly positive predictor of success, and age is still a significantly negative one:
One area of future analysis would be to see how teams led by young coaches differ stylistically from the norm. If, for instance, younger coaches are more likely to embrace analytics, we might expect their teams to shoot more threes.
For now, this much is clear: it’s good to be young, but it’s even better to be experienced.