Player Efficiency Rating is an awesome stat.*** Created by ESPN's John Hollinger, it's a convenient way to take into account a number of advanced metrics and come up with one number that gives you a good idea of a player's offensive efficacy.
Tom Haberstroh from ESPN made a striking chart showing how far ahead LeBron James is this year. Measuring with PER, he's having one of the greatest seasons of all time — his 30.6, if it holds, would give him only the 16th 30+ PER season, though he's already done that twice. (He's one of only four players to accomplish the feat more than once, along with Wilt Chamberlain, Michael Jordan, and Shaquille O'Neal.)
So, good for LeBron! A separately interesting question, though, is who's having the worst season. Looking at the chart, Jason Collins and Eddy Curry immediately jump from the page, but that's boring — they've played statistically insignificant minutes. To truly decipher the league's least effective player, you have to pick someone who's played a considerable number of minutes.
Basketball-Reference.com has PERs for 472 players this season. For those players, the median number of minutes accumulated — don't look at minutes per game, because that's skewed by injuries and other factors — is 912, between J.J. Barea's 914 and Carl Landry's 910.
That means if we're looking to find the worst player in the league, we can ignore the grossly low PERs of players like Jason Collins, Jamaal McGloire, Luke Walton, Ryan Gomes, and Jannero Pargo, none of whom have played more than 425 minutes this season or been meaningful parts of their teams.
DeShawn Stevenson, on the other hand: now here's a candidate. As a shooting guard on the abysmal Nets, Stevenson has started 29 games and played in 48. His 916 minutes played put him at almost exactly the league median. And last year, he featured to some extent on the championship-winning Dallas Mavericks. Also, let's not forget that time he famously called LeBron James "overrated" and taunted him when he was back with the Wizards.
His PER in 2012? 4.6.
When the league average is mathematically fixed at 15.0, this is really terrible. It's so terrible, in fact, that, measuring in this way, Stevenson takes the worst-player honor in a landslide. The next closest who exceeds the minutes-played league median is Derek Fisher, at 7.6 over 1423 minutes. DeShawn Stevenson has his 29.1 FG%, 28.8 3pt%, 2.0 rebounds, and 3.0 points per game to thank for the honor.
But wait: is Stevenson a great defender? Is he compensating on the other side of the ball? Nope! His defensive rating is 112, good for 21st-worst in the league. (Only six players above the league median in minutes are worse than him: Jimmer Fredette, D.J. Augustin, John Salmons, fellow Net Anthony Morrow, and Isiah Thomas.)
So, congratulations, Deshawn. At least you have Abe Lincoln tattooed on your neck.
***PER isn't perfect; it doesn't really take into account defense, since that's harder to quantify. And some say it rewards volume shooters. Here's the formula below, in case you're curious; you can do more reading at the PER wiki.