A Fraction of the Sum
Last week, I set out to write a fawning post on Lamar Odom and how vastly under-appreciated he seems to be, particularly among GMs. So, like any good researcher, I set out to search for evidence that would support the conclusion I had already reached. I figured Hollinger's Player Efficiency Ratings, a frequent stop for bearers of unconventional wisdom, would be a good place to start. Upon finding that during the 06-07 season Lamar sported a surprisingly average PER of 16.1, I realized I would have to revise my angle. My first thought was that this was further evidence that despite his obvious virtues, maybe Lamar really is just a bad fit on the Lakers alongside Kobe. But after doing a little more digging and discovering that Lamar's PER was worse than the likes of Brent Barry, Earl Boykins, Bernard Robinson, etc., I came to the conclusion that the problem doesn't lie with Lamar or the Lakers' system, but with Hollinger's system and the thinking that goes behind new stats.
While spending a half-hour trying to decipher what caused his PER to drop 1.2 over the past two years, I started to realize one of my problems with stats of its ilk. Despite the limitations of traditional stats, we understand their flaws and can reasonably discuss them while keeping their limitations in mind. We know that the quality of a player's teammates will affect his assists, that a team's pace will skew its numbers, that a player's height should be considered when looking at rebounds (thanks FD), etc. Because we understand the limitations of these numbers, we can use them reasonably when discussing the impact of various players. With PER, on the other hand, nobody (or very few of us, I should say) understands it well enough to even know its problems. Maybe that's our problem, and the stat's been around long enough that the onus is on us to figure out its strengths and weaknesses, but, seriously, look at this monstrosity:
uPER = (1/MP)*
+ (2 - factor*(tmAST/tmFG))*FG
+ (FT*0.5*(1 + (1 - (tmAST/tmFG)) + (2/3)*(tmAST/tmFG)))
- VOP*DRBP*(FGA - FG)
- VOP*0.44*(0.44 + (0.56*DRBP))*(FTA - FT)
+ VOP*(1 - DRBP)*(TRB - ORB)
- PF*((lgFT/lgPF) - 0.44*(lgFTA/lgPF)*VOP) ]
Keep in mind that's just for the unadjusted PER. That equation still has to be adjusted for pace, and then normalized around 15. As an econ major who's had to take more than his fair share of stats classes, I'm still not capable of breaking down that equation in any meaningful way.
Now, this isn't intended to be a simple "PER sucks because it's complex" rant. My main problem with PER -- and a lot of the modern era stats -- is that by attempting to reveal truths by combining numbers, they often obscure most of the story. For example, I've never been a fan of relying on numbers that have been adjusted for minutes played. Rather than telling me that Ike Diogu averaged 22 points per 40 minutes during his time at Golden State this year, I'd much rather know that he averaged 7.2 points per game while averaging only 13.1 minutes. By combining those numbers, you lose a part of the story. Trying to extrapolate what someone does in limited time by assuming he could continue that production if just given a chance is terribly faulty logic. Unless you're David Lee, most players don't get buried on the depth chart without a reason. It's exactly that kind of reasoning that leads Hollinger to make ridiculous statements like Indiana got the best of the Harrington/Jackson trade.
That per-40-minute nonsense also makes it so Dajuan Wagner's PER was 17.2, Julius Hodge's was 16.0, and Pape Sow's was 16.4. In other words, without knowing a whole lot more about a player's statline, just glancing at their PER will often be completely useless. But isn't the whole point of the number to boil a player's statistical contributions down to one easy-to-reference number? By consolidating stats into more complex measures, you gain the ability to compare across players, but you lose explanatory power. Obviously there's a balance to be struck with this trade-off: for example, if given the choice between knowing a player's field goal percentage or his field goals made and field goals attempted, I'd take the former because it allows for clearer comparisons across players. PER simply takes that kind of thinking to the extreme. What is sacrificed by this metric is rarely worth what is gained.
As usual, I'd like to end this rant with a few disclaimers. I'm not saying I can't ever appreciate what Hollinger and APBRmetrics accomplish. For instance, in a recent post for TrueHoop, Kelly Dwyer used Penny Hardaway's 99-00 PER to explain that he had a quality year; in that case, writing ten stats would have been overkill. When trying to evaluate a player, 82games or Basketball Reference is almost always my first stop. Taking into account the extra value of free throws and 3-pointers when calculating a player's eFG% is a nifty trick. You very well might catch me referring to someone's PER at some point in the near future and will want to cry hypocrisy. But in the end, if you're going to take the time to analyze a player in depth, you might as well look at his entire statline to get the complete picture.