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The player efficiency rating (PER) is John Hollinger’s all-in-one basketball rating, which attempts to boil down all of a player’s contributions into one number. Using a detailed formula, Hollinger developed a system that rates every player’s statistical performance
PER strives to measure a player’s per-minute performance, while adjusting for pace. A league-average PER is always 15.00, which permits comparisons of player performance across seasons.
PER takes into account accomplishments, such as field goals, free throws, 3-pointers, assists, rebounds, blocks and steals, and negative results, such as missed shots, turnovers and personal fouls. The formula adds positive stats and subtracts negative ones through a statistical point value system. The rating for each player is then adjusted to a per-minute basis so that, for example, substitutes can be compared with starters in playing time debates. It is also adjusted for the team’s pace. In the end, one number sums up the players’ statistical accomplishments for that season.
Relationship to baseball sabermetrics
Hollinger’s work has benefitted from the observations of sabermetric baseball analysts, such as Bill James. One of the primary observations is that traditional counting statistics in baseball, like runs batted in and wins, are not reliable indicators of a player’s value. For example, runs batted in is highly dependent upon opportunities created by a player’s teammates. PER extends this critique of counting statistics to basketball, noting that a player’s opportunities to accumulate statistics are dependent upon the number of minutes played as well as the pace of the game.
Problems with PER
PER largely measures offensive performance. Hollinger freely admits that two of the defensive statistics it incorporates—blocks and steals (which was not tracked as an official stat until 1973)—can produce a distorted picture of a player’s value and that PER is not a reliable measure of a player’s defensive acumen. For example, Bruce Bowen, widely regarded as one of the best defenders in the NBA (at least through the 2006–07 season), has routinely posted single-digit PERs.
“Bear in mind that this rating is not the final, once-and-for-all answer for a player’s accomplishments during the season. This is especially true for players such as Bruce Bowen and Trenton Hassell who are defensive specialists but don’t get many blocks or steals.”
Some have argued that PER gives undue weight to a player’s contribution in limited minutes, or against a team’s second unit, and it undervalues players who have enough diversity in their game to play starter’s minutes.
PER has been said to reward inefficient shooting. To quote Dave Berri, the author of The Wages of Wins:
“Hollinger argues that each two point field goal made is worth about 1.65 points. A three point field goal made is worth 2.65 points. A missed field goal, though, costs a team 0.72 points. Given these values, with a bit of math we can show that a player will break even on his two point field goal attempts if he hits on 30.4% of these shots. On three pointers the break-even point is 21.4%. If a player exceeds these thresholds, and virtually every NBA player does so with respect to two-point shots, the more he shoots the higher his value in PERs. So a player can be an inefficient scorer and simply inflate his value by taking a large number of shots.”
Hollinger responded, via a post on ESPN’s TrueHoop blog:
Berri leads off with a huge misunderstanding of PER—that the credits and debits it gives for making and missing shots equate to a “break-even” shooting mark of 30.4% on 2-point shots. He made this assumption because he forgot that PER is calibrated against the rest of the league at the end of the formula.
Actually, if we took a player that was completely average in every other respect for the 2006–07 season—rebounds, free throws, assists, turnovers, etc.—and gave him a league-average rate of shots, and all of them were 2-pointers, and he shot 30.4%, he’d end up with a PER of 7.18. As long-time PER fans know, that would make him considerably worse than nearly every player in the league.
To end up with a league-average PER of 15.00, the actual break-even mark in this case is 48.5%, which is exactly what the league average is on 2-point shots this season.