Using a detailed formula, Hollinger developed a system that rates every player's statistical performance.
[1] 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 positive results, including field goals, free throws, 3-pointers, assists, rebounds, blocks and steals and negative results, including 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.
In the end, one number sums up the players' statistical accomplishments for that season.
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.
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 through the 2006–07 season, 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.
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.
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.
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.Hollinger has set up PER so that the league average, every season, is 15.00, which produces sort of a handy reference guide:[2] Only 33 times has a player posted a season efficiency rating over 30.0 (with more than 15 games played in that season), with the highest score being 32.85 (Nikola Jokić).
Michael Jordan, LeBron James, and Nikola Jokić lead with four 30+ seasons each, with Shaquille O'Neal, Wilt Chamberlain, Giannis Antetokounmpo, and Joel Embiid[3] having accomplished three each, Anthony Davis having accomplished two, and David Robinson, Tracy McGrady, Dwyane Wade, Stephen Curry, Russell Westbrook, Chris Paul, and James Harden with one.
[7] The debate was intensified on 1 October 2013, with Jordan stating that he would have liked to have played against LeBron, and believes he would have won a one-on-one encounter.
[8] Several news features focus on comparing the two players by using the PER metric.
[9][10][11] At the conclusion of the 2012–13 NBA season Miami Heat head coach, Erik Spoelstra, stated that comparing players from different generations is the equivalent to comparing apples and oranges, explaining: "You'll never be able to tell [how James stacks up to Jordan or Magic Johnson] because they didn't play against each other.
"[12] Comparing players from different generations using PER presents several problems, this is primarily due to the rule changes and the changes in statistical data collected from different eras (although many other factors could be taken into consideration, even down to the increased sample size as the NBA grew through incorporating more teams).
Some of the more important rule changes that should be considered include; some of the players on this list, such as Wilt Chamberlain and Bill Russell, played before the three-point shot, blocks, and steals stats were officially recorded.
Blocked shots and steals were first officially recorded in the NBA during the 1973–74 season.
The 2004 rule changes, which also included calling the defensive 3 second rule ("a defensive player may not station himself in the key area longer than three seconds"—a longstanding rule which had been ignored by referees) had a major effect, opening up the game and allowing a more free-flowing offense; it encouraged aggressive inside attack based plays (to draw fouls), and has increased the number of fouls given when contact is made on players who drive to the basket.
Where With Once uPER is calculated, it must be adjusted for team pace and normalized to the league to become PER:
This final step takes away the advantage held by players whose teams play a fastbreak style (and therefore have more possessions and more opportunities to do things on offense), and then sets the league average to 15.00.
Also note that it is impossible to calculate PER (at least in the conventional manner described above) for NBA seasons prior to 1978, as the league did not keep track of turnovers among other advanced statistics before that year.