Tuesday, August 25, 2009

The evolution of a player efficiency system

The other day I was going through some old junk in my room when I stumbled upon a long-forgotten collector's item: the Premiere Issue of Rip City Magazine from November 1992.

Inside the issue, there was a long feature on Clyde Drexler's experience at the Olympics, a Q & A with the newly-acquired Rod Strickland ("I'm looking forward to going back home to New York City with a championship ring on my finger.") and a bold prediction by Mike Rice that Dikembe Mutombo would be a bust (Short answer: he wasn't).

As I was flipping through it, I got to an article by Pat Lafferty called "Inside Player Ratings." In it, Lafferty describes the increase in the use of player efficiency evaluation.

"In the age of computer technology," he wrote "most clubs measure the production of their own players and those on other teams as well."

He wrote that one formula being used to measure player efficiency did so by adding the positive stats of a player (points, rebounds, assists, steals, blocks), subtracting the negative ones (missed shots, missed free throws, turnovers, and 50 percent of fouls), and dividing the net figure by minutes played, thereby giving a performance grade for each player per minute.

Michael Jordan, for example, was the league's most efficient shooting guard, with an efficiency rating of .769. David Robinson was the most efficient center, with a rating of .814. And in large part, the system was very effective in charting the efficiency and value of the league's top players, especially when viewed nearly 20 years after the fact.

But as I read all of this, I thought "well this sounds familiar." And then I remembered John Hollinger.

Hollinger is ESPN's resident basketball statistical genius, and rose to fame after creating the Player Efficiency Rating, or "PER" for short. PER has been widely viewed as the sabermetrics of basketball, and is taken to be a very accurate account of measuring the offensive efficiency of NBA players in a way that normal individual stats cannot. Hollinger has used his PER every year to chart NBA player efficiency, and has been a go-to-source in recent years for anyone who wants to see if a player is as good as the numbers say he is.

In his words, this is how he measures PER: "To generate it, I created formulas ... that return a value for each of a player's accomplishments. That includes positive accomplishments, such as field goals, free throws, 3-pointers, assists, rebounds, blocks and steals, and negative ones, such as missed shots, turnovers and personal fouls. Two important things to remember about PER is that it's per-minute and pace-adjusted."

The two ratings systems are remarkably similar on the surface, with Lafferty's formula already in use nearly 10 years before Hollinger discovered PER. No one had ever even heard of a Player Efficiency Rating until Hollinger came around, and yet, tucked away on a two-page spread in a 1992 Portland Trail Blazers fan magazine, was a system that seemed to have been built on the same concept. Curious, I went about comparing the two formulas to see how much the two shared.

If you look closer at the actual formula that is used to calculate PER, Hollinger's is slightly modified. In Hollinger's equation, there are some fractions and percentages thrown in, as well as league averages in various statistics and a league-wide PER set at 15.00 PER also adjusts for a team's pace, because a fast-break team will have higher statistics than a team that plays at a slower pace (and I'm not even going to begin to describe how pace is factored into the equation).

Working with only the general description that Lafferty gives the 1992 formula, I can't say with certainty whether it goes more in-depth than the simple formula he described. But I think it's fascinating how something that was so simple and obscure 20 years ago turned into the most talked-about statistic today. Hollinger took something that just barely scratched the surface of player efficiency, altered it, adjusted it, expanded it, and made it into something more in-depth and complex.

Yes, Hollinger invented his PER, but the concept of a player efficiency system dates back to the years when Hakeem Olajuwon was patrolling the paint and Kevin Johnson was manning the point. Even in 1992, years before Hollinger even stepped on the scene, there was a system that accurately measured which players were better than others; creating a numerical value to take the place of personal fan debates.

But it never became popular until Hollinger's updated version was developed. In the cases where an efficiency system was used, it was relegated to fan newsletters or someone's blog. No matter what the system was or how they differed, it wasn't taken seriously, and didn't catch on in the mainstream. Maybe fans weren't ready for it in 1992, or maybe PER caught on because of the rise of the popularity of sabermetrics in baseball.

Now, it seems like efficiency matters more than individual stats like points and rebounds, and is used as a more effective tool for measuring a player's value. Any way you look at it, the concept was there, it only needed to be refined and revised, which Hollinger did with great success.

I'll bet that back in 1992, Lafferty and Rip City Magazine had no idea that the small concept they used in a filler piece would take off the way it did.

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