Saturday, January 17, 2009

Saturday's Fun with Plus/Minus, Edition II

The plus/minus stat continues to confuse/frustrate us. Stat-heads celebrated when ESPN followed NBA.com and Yahoo's lead and added it to its box scores, but we're not convinced plus/minus, at least on an individual game level, means anything. Last Saturday, we looked at one strange plus/minus line suggesting that Jamal Magloire had a huge positive impact in limited minutes for an otherwise uninspired Heat team. We concluded that Magloire had been OK, but that his plus/minus numbers were likely the result of his happening to be on the court when Dwyane went crazy--twice. 

This week, we noticed another interesting plus/minus line from the Heat's 102-99 win over the Bucks on Wednesday, this time involving two teammates. In 40 minutes, Andrew Bogut finished plus 11 in the loss. In 37 minutes, Michael Redd finished minus 10. How could two players who play so many of the same minutes have such drastically different plus/minus scores? We checked the game log to find out, and what we found didn't surprise us: Nearly the entire difference can be explained by one nine-minute stretch in which Redd was on the court and Bogut was not. 

The Bucks were up 18-8 when Skiles replaced Bogut with Dan Gadzuric with 5:18 left in the first quarter. When Bogut re-entered the game at the 9:32 mark of the second quarter, the Heat were up 36-28--an 18-point swing. For all but a few of their remaining minutes, Bogut and Redd were on the court together. 

Three questions need to be asked, then:

1) How much did Bogut contribute to that early lead?

2) Why did the Bucks fall apart without him for nine minutes?

3) Was Redd really that bad for that nine-minute span? 

The answer to question one is unclear (I didn't watch the game). Bogut had one basket and a couple of boards as the Bucks jumped out early. Miami started cold, going 3-11, and it's reasonable to conclude Bogut contributed to that; several sets of numbers show the Bucks D performs much better with Bogut on the floor.

The answer to question two is easy: Miami went off from the perimeter (jumpers from Beasley and Marion, and five threes from Daequan Cook, who's playing so well he may merit his own post soon. Chris Quinn chipped in a three as well). 

As for the last question, Redd went 0-4 during the nine-minute span. It's unclear who he was guarding on the other end, but Redd's never been regarded as a good defensive player. 

Overall, Redd scored 16 points, but it would have been hard for him to score those points less efficiently. He was 8-21 from the floor, attempted zero free throws, grabbed one board and recorded zero assists. He also committed five fouls. Redd did have two steals against one turnover, but, in general, it appears Redd deserved a minus 10 for the night. 

Did Bogut deserve a plus 11? That's less clear. 

By the way, for the year, Redd leads the team in plus minus. Broken down further, the stats show Milwaukee performs much better offensively with Redd on the court and at about average levels (for them) on defense. So when Redd sputters on offense, he can turn into a liability--which is what happened Wednesday. 

So does that mean plus/minus actually works? My head hurts. 






1 comment:

  1. Love your example and analysis. You know I am a big fan of the +/- stat, and I actually think that your example backs it up. Hey, if the Bucks were up by ten early with Bogut in the game, and when he re-entered the game, they were down 8, that tells me that he made a positive difference when on the court. I also didn't see the game so I don't know what it was, but the fact of the matter remains, his TEAM was better with him on the floor than with him on the bench, and by quite a bit. That tells me he was valuable to the Bucks on that given night against that given opponent.

    In hockey, when the Red Wings score and Lidstrom's on the ice, no one asks which line the Red Wings were skating against, or who else was on the ice at the time. Similarly, when the Red Wings allow a goal with Lidstrom on the ice (seldom), it really doesn't matter if it was the other team's first line or fourth line scoring it.

    The point remains, hockey (and basketball) is a TEAM sport. The player's TEAM either scored or got scored on when this player was on the ice (or on the basketball floor). That's all there is to know, and that's all you really need.

    One game may be misleading, but over a big-enough size sample (20 games ? 40 games ? 80 games ?), the cream will rise to the top in terms of plus/minus. To prove my point, I will direct you to the last 10-20 years of NHL Final Regular Season statistics (available at nhl.com, espn.com, etc..) Look at the top 10-20 players in season-long +/-. You won't find a bad player on these lists, and actually, most of them will probably be players considered to be the top 20-40 in the game. (Then also look at all-time CAREER plus/minus. Once again, all of these players are absolute superstars)

    I believe the same can be said about the NBA stats (again, over a long enough size sample such as a full season). After we have 20-30 years of stats in the bag on this, you should see the same trend as in hockey.

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