In professional basketball, the most commonly used statistical benchmark for comparing the overall value of players is called efficiency. It is a composite basketball statistic that is derived from basic individual statistics: points, rebounds, assists, steals, blocks, turnovers and shot attempts. The efficiency stat, in theory, accounts for both a player's offensive contributions (points, assists) and their defensive contributions (steals, blocks), but it is generally thought that efficiency ratings favor offense-oriented players over those who specialize in defense, as defense is difficult to quantify with currently tabulated statistics.
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EFF
The NBA publishes online all the basic statistics recorded officially by the league. Individual player efficiency is expressed there by a stat referred to as 'efficiency' and abbreviated EFF. It is derived by a simple formula:
(PTS + REB + AST + STL + BLK − Missed FG − Missed FT − TO) / GPThe current NBA efficiency leaders (EFF) list is here.
The formula was created by Kansas City sports reporter and statistician Martin Manley (1953–2013).
PER
The most commonly used alternative to the EFF is the player efficiency rating developed by ESPN basketball statistician John Hollinger. It is denoted as PER, and is derived by a very complex calculation designed to compensate for different teams' varying style of play, among other factors. PER scores do not differ markedly from EFF scores, but player rankings will not be the same in both systems.
A PER of 15 is considered average across the entire league (not true of EFF), and serves as a simple benchmark against which any player may be quickly compared to indicate his approximate net worth to an NBA franchise. Teams intending to compete for the championship typically seek to enlist at least two star players with high efficiency ratings above the low twenties.
A PER of 30 over a span of more than a few games is considered exceptionally high. According to the modified PER formula used at Basketball-Reference.com, the highest PER ever achieved over an entire single season in the NBA was 31.84 by Wilt Chamberlain in 1962/63. No other player surpassed 30 until Michael Jordan in 1987/88 with a PER of 31.71. Since then, Jordan repeated the accomplishment three more times, and the milestone has also since been eclipsed by David Robinson, Stephen Curry, Shaquille O'Neal (three times), Tracy McGrady, Dwyane Wade, LeBron James (four times) and Anthony Davis. No PER statistics are available pre-1951/52 as the 'minutes played' statistic was first recorded during that season.
Some currently active NBA players known for consistently high efficiency ratings include, LeBron James, Chris Paul, Russell Westbrook, Dwyane Wade, Kevin Durant, Dirk Nowitzki and Dwight Howard.
Player efficiency rating NBA records:
EuroLeague and EuroCup
The EuroLeague, its second-tier level competition, the EuroCup, and several European national domestic leagues, use a different type of formula to determine the ratings and efficiency of players, called the performance index rating (PIR):