the numbers

I tried to pick an easier productivity metric to start, and at least at first glance, the NBA Efficiency metric looks to be that.

NBA.com evaluates all players based on the efficiency formula: ((Points + Rebounds + Assists + Steals + Blocks) - ((Field Goals Att. - Field Goals Made) + (Free Throws Att. - Free Throws Made) + Turnovers)).

However, when I started giving it more thought and reading what others had to say about it, I started to realize that it was much more complicated than I first imagined.  Two points in particular are interesting to discuss here: first is the value applied to scoring opportunities and the second is the value of gaining or keeping possession of the ball.  For example, points, assists, field goals, field goal attempts, free throws, and free throw attempts would all be associated with scoring.  On the other hand, rebounds, steals, blocks and turnovers all relate more to possession of the ball.

This raises the question of how to value scoring and possession relative to each other when trying to maximize a team’s wins.  How much is a rebound worth compared to a field goal?

David Berri speaks of this issue on his blog.  Some people criticize Berri for giving too much value to rebounds, and that the value a rebound receives in a calculation such as the NBA Efficiency Rating is much more accurate.  One of Berri’s arguments against this is that it is important to appropriately account for shooting percentage.  For example, if points are weighted too much relative to possessions (rebounding, steals, blocks, turnovers), then this will give an advantage to prolific shooters rather than “efficient” shooters.

For example, if one rebound is equivalent to one point, as it basically is in the NBA Efficiency metric, then a player will break even shooting 25% from 3-pt range, and 33% from 2-pt range.  If he hits one out of four 3 pointers, he gets 3 points and the opponent can acquire 3 rebounds, which cancel out the points.  Therefore, by taking more shots from any range, the frequent shooter will increase his NBA Efficiency Rating despite not being a great percentage shooter.

I am not saying that I feel that Berri’s analysis is bullet-proof either, but I just wanted to point out some of the interesting issues that I learned while diving into the statistic known as the NBA Efficiency Rating.