For those that don't know, I'll be doing a series of blogs about advanced basketball stats.  Today, I'll talk about John Hollinger's Player Efficiency Rating (PER) stat because it is the most popular of the new advanced stats, the one that is becoming an accepted part of the basketball language.  I spend a lot of time on basketball message boards, and I have been seeing more and more people reference PER as a way of ranking players.  There are pros and cons to using PER, though, many of which are due to incorrect usage (many Know-it-Alls and Skeptics either misuse or malign the measure).  So let's see if we can shed some light on things.

What is it: PER actually measures a combination of production and efficiency.  It looks at information found within the box scores (such as all of the fantasy stats), adjusts for team pace and individual minutes played, and normalizes based upon numbers across the league (league average PER is always set to 15).  The end result is a measurement that helps quantify many of the accomplishments that comprise a productive, efficient player (especially on offense).  For those that want more technical information on how PER is calculated, it can be found here.

Strengths: PER is a single number, which makes it easier to use to compare two players than looking at combinations of points/rebounds/assists/blocks/steals/percentages/etc.  Also, by normalizing for minutes played and pace, PER allows players in different situations to be compared more logically.  Finally, because PER is normalized to the league average it gives a way to compare players across time.  For instance, PER can't tell us who was actually better between Shaq and Kareem Abdul-Jabbar…but it can tell us that over their careers, Shaq has been more statistically dominant with respect to his peers (career PER of 27.01) than Kareem was with respect to his peers (career PER of 24.58).

Weaknesses: PER does not account for defense outside of blocks/steals/rebounds, which would be a limitation for it being a "total player ranking" as it barely addresses half of the game.  It doesn't address at all whether a player limits his opponents to worse statistics, or how the team's defense performs with that player on the court.  Players like Bruce Bowen, for instance, that made their careers based upon strong defense are generally underrated by PER.  Likewise, PER does not take into account how an individual player's numbers translate into team success, another weakness for using it as a stand-alone player rater.  Finally, because PER is normalized per minute played, looking only at PER can deceptively rank a bench player that plays very limited minutes above an impact starter.

Usage:  You can't simply say "player X has a higher PER than player Y so he is better".  Instead, you can use PER to say that player X has been more statistically productive than player Y, and from there you need to look to personal observations or other statistics to help determine how factors like defense, teammate quality, or team role would affect the measurement.  For instance, one can look at Michael Jordan's PER of 31.1 in 1988-89 and Kobe Bryant's PER of 28.0 in 2005-06 and surmise that Jordan was more statistically productive with respect to his peers in 1989 than Bryant in 2006.  But to truly try to gauge who was the better player those years, other stats that fill the holes of PER should be used.  PER is a great way to make a quick first comparison when trying to gauge players, but (like all stats) should always be used only as evidence within an argument and not as the argument itself.

Leaders: As of 1/6/09, the current leaders in the NBA in PER this season are:

James' PER, if he can maintain it, would be the highest in NBA history.  The current high mark is 31.84 from Wilt Chamberlain in 1962 - 63 (Wilt has the two highest marks ever).  Jordan comes in with the third highest PER in history, 31.71 in 1987 - 88.  Here are the league leaders in PER for every season since 2000:

Next time: the +/- stat