Monday, March 5, 2012

LeBron James: Why His PER Is Useless Information


LeBron James' success is measured by winning and championships, so his PER is irrelevant bullshit produced by ESPN's hype machine.

There's been a lot of talk that LeBron is having the greatest season in NBA history because an obscure number that no one understands says so. That number is his Player Efficiency Rating (PER) and examples of that talk can be found in the following articles:

The creator of PER, ESPN columnist John Hollinger, said in the video posted above that PER was complicated. Well, sports economist David Berri recently posted his thoughts on this analysis of PER done by former Dallas Mavericks consultant Wayne Winston: Wayne Winston Simplifies PER. Here's an excerpt on PER's complexity:
Wayne Winston has a short post on John Hollinger’s Player Efficiency Rating. Hollinger’s PER Ratings Demystified
Here is Wayne’s entire post (in case you didn’t feel like clicking over): 
I have had a great time teaching a sports and math class to Kelley School of Business students at Indiana University. One of my ace students Paul Aynilian did a study trying to estimate John Hollinger’s famous ESPN PER Ratings based on box score statistics. 
We found that 45.75*(Points/Minute)+22.55*(Rebounds/Minute)+32.8*(Assists/Minute)+58.2*(Steals/Minute)-48.65*(Turnovers/Minute) -39.73*(Missed FG’s per minute) -20.6*(Missed FT per minute)+38.37*(Blocked Shots Per Miute)-18.68*(Personal Fouls Per Minute) explains over 99% of the variation in this season’s PER rankings and is off by an average of .37 in estimating the PER of the top 200 NBA players whose stats are on Yahoo.com. So basically our simple formula virtually duplicates the PER rating without a lot of mumbo jumbo. 
The disturbing thing about these weights is that if an NBA player shot 33 .33% (1-3) then the more shots they take the higher their PER because shooting 1 for 3 gives you a net contribution of 2(45.75)-2(39.73)>0!! Clearly this is bad because a 33% shooter is not a good shooter and with these weights the more shots a bad shooter takes, the higher his PER rating. 
Let me add a bit to this story...  
1. PER certainly looks like a very complicated formula. And so it is easy for people who are not mathematically inclined to think it is 'advanced' (although it is highly correlated with the much simpler NBA Efficiency metric – which few people think is 'advanced').
2. Measures like PER and NBA Efficiency are not about 'efficiency'. But they do explain – as noted in Stumbling on Wins — player evaluations. In other words, these “advanced” measures are consistent with popular perceptions."

OK, so PER is a complicated-looking way of measuring player efficiency by... requiring them to shoot better than 33% from the floor? Good thing it looks complicated  because it sounds stupid.

Hollinger said in the Microsoft Business Intelligence interview that offensively, PER absolutely correlates with winning. Is that all it takes to win in the NBA - shooting better than 33% from the floor? Then why have the Charlotte Bobcats only won 4 games this season scoring points with a 44% shooting efficiency?

Berri explained the problem:
"We can also see how well PER explains wins with a simple regression of team wins on a team’s PER. The results indicate that PER only explains 33% of team wins. You can do better if you add the team defensive measures used in Wins Produced. Those factors increase explanatory power to 55% (if you weigh the team defensive factors as they are in Wins Produced) or 82% (if you allow the weights of each individual factor to vary). Either way, PER does not explain 95% of team wins (as we see with Wins Produced). 
In sum, PER is a model that is not theoretically sound (yes, it over-values inefficient scoring) or empirically sound (it doesn’t explain wins)."

So, the best season of LeBron's career is supposed to be measured by a statistic that isn't theoretically or empirically sound? That only makes sense in the theater of the absurd that surrounds the Miami HEAT featuring shows debating crunch time plays in exhibition games.

At the end of the day, that's all the talk about LeBron's PER is - another piece of content produced for ESPN's talking heads to debate and hate on LeBron. They're not the Wordwide Leaders of the HEAT Shit List by accident.

For more information on PER and Game Score, the simpler version of PER discussed in the Business Intelligence video (what an ironic sponsor),  see the FAQ at Berri's website - wagesofwins.com. For a better story about the historical context of LeBron's season, check out this article by the Courtside Analyst.

Remember: PER's garbage and Hollinger's hustling it for money and fame just like the stat geeks hustling plus/minus models to NBA franchises. Don't Believe the Hype.

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