Player Efficiency Rating - Problems With PER

Problems With PER

PER largely measures offensive performance. Hollinger freely admits that two of the defensive statistics it incorporates -- blocks and steals -- 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."

The formula of PER requires adding values with different units which is prohibited by unit analysis. For example, the formula adds assists to rebounds with no conversion factor.

In addition, 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.

Lastly, PER rewards 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."