Adjusted Plus-Minus: Measuring Defensive Effectiveness

money puck
October 20 2014 12:45PM

#468441193 / gettyimages.com

Alex Edler: actually pretty good at preventing quality shots

Most people in the stats community dislike plus-minus, but my feelings are much stronger than that. I loathe plus-minus. It’s personal. The draft for my keeper league hockey pool was about to start and I was considering taking a flyer on a young Erik Karlsson. He was coming off his 2nd season in the NHL, where he posted an impressive 45 points. However, at minus 30 I figured he must be in for a significant drop in playing time considering he was obviously such a huge defensive liability to his team. Karlsson ended up finding himself on the roster of my arch nemesis, scored an insane 78 points, and hilarity ensued. I hate plus-minus.

In theory, plus-minus should be an immensely useful stat. The team who scores the most goals in a game wins, so by extension it seems to make sense that better defensive players would be on the ice for more goals for than goals against. Unfortunately, because this statistic is so greatly affected by goaltending and team’s on-ice shooting percentage, amongst other factors, the usefulness of plus-minus is negligible and it has been largely abandoned by the stats community.

This got me thinking: while we know plus-minus itself is a useless statistic, is there a way we could more accurately calculate the impact a player has on their terms scoring differential? Or put more simply, can we create a better plus-minus? Read past the jump to find out.

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THE NATION MINUTE

Nation World HQ
October 20 2014 11:45AM

The Nation Network brings you the Nation Minute, a rapid fire look at stats and news around the network or NHL. On tap this week: The Canucks offense, Jonas Hiller, Ben Scrivens, Mark Fayne and more.

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THE FANTASY MINUTE: WAIVER WIRE

Nation World HQ
October 18 2014 10:23AM

The Nation Network and Dailyfaceoff present the Fantasy Minute. A quick run through the best Fantasy Hockey waiver adds and sleepers for the week. 10.17.14 (Based on 12 team leagues)

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THE ROUNDUP

Nation World HQ
October 17 2014 08:00AM



Jonas Hiller seeing beach balls, the Oilers aren't very good at hockey, the Leafs could use Eric Staal, the impact of defense on goaltender stats, loving the game again and more in this weeks Roundup.

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Adjusted Save Percentage: Measuring the Impact Defense has on Goaltending Statistics

money puck
October 16 2014 01:30PM

#456882700 / gettyimages.com

One of the reasons we love sports as much as we do is because of the great debates it can spawn. I came across a classic hockey debate the other day in relation to Ryan Miller. “Of course Miller didn’t post elite numbers last year. He played for Buffalo!”   

As I was thinking about this, it struck me that while we have made huge strides in advanced statistics overall, we haven’t made much progress in terms of quantifying the impact of defense and separating that contribution to statistics for the goalie themselves. We can tell the percentage of shots a goalie save (SV%), but we have little to no insight into the difficulty level of the shots themselves.  

From a quantitative standpoint, we understand the game better now than ever before. We understand shot attempt differential, which we know we can be used to approximate possession. We call this corsi, and we understand this to be a key component of overall team success. We can also begin to isolate the impact a player has on their team’s shot attempt differential, which is a solid representation of strong two way play.

However, there is one factor that detractors of advanced stats have always struggled with. Detractors have long protested that not all shots have an equal chance of going in, and they’re right. Is it possible to adjust save-percentage to reflect easier or more difficult workload? Find out after the jump. 

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