David Berri on Adjusted Plus/Minus

1 Comment

Way back in 2006, David Berri, Martin Schmidt, and Stacey Brook came out with a book called The Wages of Wins. It was supposed to be Moneyball for sports other than baseball, but for a lot of people, the book read like Moneyball with a serious chip on its shoulder. In a team game with lots of variables, Berri and his co-authors were confident in their regression-based assertions that  there were 90 players more valuable than Allen Iverson during the season that he won MVP, that scoring was vastly overvalued while rebounding was too often neglected, and Ray Allen had been just as good throughout his career as Kobe Bryant. 

The general feeling among a lot of hard-core basketball fans and analysts was that the Wages of Wins system, which relied only on box-score based statistics, couldn’t possibly accurately capture everything that made a player valuable in a five-on-five game. The logical extreme of that philosophy came in the form of Wayne Winston, the former stat guru for the Dallas Mavericks whose brainchild was adjusted plus/minus, which sought to measure a player’s value without using any box-score statistics whatsoever. As it turned out, he had some even more outlandish conclusions than Berri and co. did. He said that the Knicks should never have traded Tim Thomas, that Lamar Odom was better than Kobe Bryant, and that Kevin Durant wasn’t helping the Thunder win. 
After last weekend’s Sloan stats and analytics conference, David Berri has a short post up on adjusted plus/minus. Here’s the crux of Berri’s argument for box-score bases metrics over adjusted plus/minus:
JC Bradbury and I – in a forthcoming article in the Journal of Sports Economics — report that only 7% of a player’s adjusted plus/minus is explained by what a player did the previous season (oddly enough, unadjusted plus/minus has a stronger – albeit still relatively weak – correlation).  In other words, the correlation coefficient for adjusted plus/minus from season-to-season is below 0.30.   And when we look at players who switch teams – as Songaila did – we fail to find a statistically significant relationship. In contrast, any measure (PERs, Wages of Wins measures, NBA Efficiency, Win Shares, etc…) based on the box score will have a correlation coefficient of at least 0.65, and often these marks are above 0.80. 

Berri makes a solid point. He uses Darius Songalia as a case study for how inconsistent adjusted plus/minus can be, but he could easily have used Kevin Durant, who started the season as a posterchild for how plus/minus based stats could contradict box score metrics but is now an example of how elastic adjusted plus/minus can be from season to season. 

I’m a big believer in using advanced stats to gain knowledge about basketball, but it appears that both Berri and Winston have holes in their metrics. Berri’s box-score based metrics don’t necessarily reflect who was doing what helped his team win the game. For example, let’s say Matt Barnes plays great defense on Kobe for 20 seconds and forces him into a tough fadeaway. Dwight Howard then blocks out Pau Gasol and keeps him from getting to the rebound. The ball caroms off the rim and goes to Vince Carter, who collects the easy rebound. In Berri’s system, only Carter gets credit for doing something right on that play. 
Winston’s system would theoretically give Barnes and Howard most of the credit for the play above. However, the issue is that they could have radically different roles on a different team. With another team, Barnes might not be a starter or a perimeter scorer, but a stretch four who provides energy and outside shooting off the bench without giving much on the defensive end. Thus, he could have a radically different value with a different team. 
Advanced statistics in basketball are wonderful, but they are far from airtight. For the foreseeable future, the best approach with advanced statistics will be to use a number of different metrics and see how they inform each other rather than wait for one perfect formula to reduce contributions to a single integer. 

Dion Waiters explains decision to sign with the Heat in an Instagram post

OKLAHOMA CITY, OK - MAY 24:  Dion Waiters #3 of the Oklahoma City Thunder reacts in the first quater against the Golden State Warriors in game four of the Western Conference Finals during the 2016 NBA Playoffs at Chesapeake Energy Arena on May 24, 2016 in Oklahoma City, Oklahoma. NOTE TO USER: User expressly acknowledges and agrees that, by downloading and or using this photograph, User is consenting to the terms and conditions of the Getty Images License Agreement.  (Photo by Ronald Martinez/Getty Images)
2 Comments

On Monday, Dion Waiters agreed to a one-year, $2.9 million deal with the Heat, far less than most people thought he would get as one of the few significant free agents still on the market. Tuesday afternoon, he posted an explanation on Instagram for his deal.

Here’s what he said:

I didn’t do it for the money… I did it for the opportunity to go out & ball & have fun. Everything else will take care of its self!!! I just felt like it was the best situation for me…& my family. I could have waited & got wat I wanted. But I rather be happy then miserable at the end of the day!!! Meaning Yu can have everything & still not be happy… #heatnation let’s get it!!! #provethemwrong #stamped #Philly

It seems clear, based on the market, that the kinds of offers Waiters was hoping for weren’t out there for him. In Miami, with Dwyane Wade gone, he’ll probably start at shooting guard and have plenty of opportunities to prove himself in hopes of landing a long-term deal next summer.

Report: Celtics sign second-round pick Demetrius Jackson to four-year deal

PHILADELPHIA, PA - MARCH 27:  Demetrius Jackson #11 of the Notre Dame Fighting Irish walks to the bench late in the second half against the North Carolina Tar Heels during the 2016 NCAA Men's Basketball Tournament East Regional Final at Wells Fargo Center on March 27, 2016 in Philadelphia, Pennsylvania.  (Photo by Elsa/Getty Images)
2 Comments

While we wait for the Celtics to make a bigger move to trade for another star, they’re filling out the end of their roster. Sheridan Hoops’ Michael Scotto is reporting that they’ve signed Demetrius Jackson, the No. 45 pick in last month’s draft, to a four-year deal.

Jackson declared for the draft after his junior season at Notre Dame. Talent-wise, he has the chance to be a major steal for Boston — DraftExpress has him ranked as the 17th-best overall prospect in this year’s draft class. But he might not play much his first year. The Celtics’ roster is already crowded and there’s still the chance that they’ll make another move with some of their much-vaunted assets if the right star becomes available.

Hawks sign former Michigan State center Matt Costello

ST LOUIS, MO - MARCH 18: Matt Costello #10 of the Michigan State Spartans handles the ball against Darnell Harris #0 of the Middle Tennessee Blue Raiders in the second half during the first round of the 2016 NCAA Men's Basketball Tournament at Scottrade Center on March 18, 2016 in St Louis, Missouri.  (Photo by Dilip Vishwanat/Getty Images)
Dilip Vishwanat/Getty Images
Leave a comment

ATLANTA (AP) — The Atlanta Hawks have signed undrafted rookie free agent center Matt Costello of Michigan State.

The 6-foot-9, 245-pound Costello averaged 5.7 points and 5 rebounds on the Hawks’ summer league team in Las Vegas.

Costello averaged 10.7 points and 8.2 rebounds as a senior at Michigan State. He holds the school’s career record with 146 blocked shots.

Terms of the deal were not released.

Watch Jamal Crawford drop an effortless 44, hit game winner at Seattle pro-am

4 Comments

Jamal Crawford knows how to get buckets.

He does it against NBA level defenders, so put him in a free-flowing pro-am — let’s say the Seattle pro-am in his hometown — and he barely breaks a sweat dropping 44. And nailing the game winner.

Doc Rivers hopes to see a lot of that next season.