All defensive stats have really huge flaws, but they're often used without any context or acknowledgement of their flaws. For example, on the last Lowe Post I heard Howard Beck of Bleacher Report casually throw out IT's Defensive Real Plus Minus (DRPM) as a reason why IT didn't get his all-star starter vote without explain what DRPM is or what a low DRPM indicates. It does make sense that Beck explained nothing - I can guarantee he doesn't know what DRPM is. I'll explain why below.
Here's why you should be cautious when using Defensive Rating, Defensive Win Shares, Defensive Box Plus Minus, and Defensive Real Plus Minus:
Defensive Rating (DRtg) - Tied extremely closely to the performance of the team. It's a viable stat to use to evaluate a team's performance but not an individual's. Additionally, DRtg is skewed positively for frontcourt players and negatively for guards.
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Example 1: Omer Asik's DRtg from years 2011-2013: 99th percentile, 99th percentile, 80th percentile. Why the huge drop off? He signed with Houston and suddenly had James Harden on his team.
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Example 2: Kawhi Leonard's DRtg spiked 6.25% from last year to this year. Why? Tim Duncan and Boris Diaw were replaced with Pau Gasol and David Lee.
Defensive Win Shares (DWS) - Relies heavily on DRtg (so it contains all the flaws of DRtg), isn't controlled for minutes played, and over-rewards guys who stuff the box score.
- Example: James Harden (2.1) and Steph Curry (2.1) both have a better DWS than Lebron (1.9), Tony Allen (1.8), and Jimmy Butler (1.9) this year.
Defensive Box Plus Minus (DBPM) - Relies exclusively on box score stats which makes it an inherently misleading stat.
- Example: Its creator openly admitted that "elite defenders based on position and communication, like Kevin Garnett and Tim Duncan, will not be properly represented" by DBPM.
Defensive Real Plus Minus - We have no idea what DRPM is. It's ESPN's proprietary formula and they haven't published it. Since Howard Beck doesn't even work for ESPN he has no way of accessing the formula, he made his allstar selection based on a black box calculation. That's indefensible.
These flaws are so glaring that, when talking about individual defenders I rely exclusively on the eye test and throw out all advanced stats that use the above metrics (specifically Win Shares, BPM, and RPM). My stance may seem extreme but I couldn't in good conscious use the above statistics without some heavy qualification. At that point I'd rather just use my eyes. Thanks for reading!
Sources:
Various pages from basketballreference.com
Submitted January 23, 2017 at 03:04PM by chatter4500