Critiquing plus/minus and corsi fairly
There is a recently posted article on BroadStreetHockey.com discussing overused and overrated statistics. The first statistic on that list is Plus/Minus. Plus/minus has its flaws and gets wildly misused at times but it doesn’t mean it is a useless statistics if used correctly so I want to defend it a little but also put it in the same context as corsi.
The rational given in the BroadStreetHockey.com article for plus/minus being a bad statisitcs is that the top of the plus/minus listing is dominated by a few teams. They list the top 10 players in +/- this season and conclude:
Now there are some good players on the list for sure, but look a little bit closer at the names on the list. The top-ten players come from a total of five teams. The top eight all come from three teams. Could it perhaps be more likely that plus/minus is more of a reflection of a team’s success than specific individuals?
Now that is a fair comment but let me present you the following table of CF% leaders as of a few days ago.
Of the top 22 players, 8 are from Chicago and 7 are from Los Angeles. Do the Blackhawks and Kings have 68% of the top 22 players in the NHL? If we are tossing +/- aside because it is “more of a reflection of a team’s success than specific individuals” then we should be tossing aside Corsi as well, shouldn’t we?
The problem is not that the top of the +/- list is dominated by a few teams it is that people misinterpret what it means and don’t consider the context surrounding a players +/-. No matter what statistic we use we must consider context such as quality of team, ice time, etc. Plus/minus is no different in that regard.
There are legitimate criticisms of +/- that are unique to +/- but in general I think a lot of the criticisms and subsequent dismissals of +/- having any value whatsoever are largely unfounded. It isn’t that plus/minus is over rated or over used it is that it is often misued and misinterpreted and to be honest I see this happen just as much with Corsi and the majority of other “advanced” statistics as well. It isn’t the statistic that is the problem, it is the user of the statistic. That, unfortunately, will never change but that shouldn’t stop us who know how to use these statistics properly from using them to advance our knowledge of hockey. So please, can we stop dismissing plus/minus (and other stats) as a valueless statistics just because a bunch of people frequently misuse it.
The truth is there are zero (yes, zero) statistics in hockey that can’t and aren’t regularly misused and used without contextualizing. That goes from everything from goals and point totals to corsi to whatever zone start or quality of competition metric you like. They are all prone to be misused and misinterpreted and more often than not are. It is not because the statistics themselves are inherently flawed or useless its because hockey analytics is hard and we are a long long way from fully understanding all the dynamics at play. Some people are just more willing to dig deeper than others. That will never change.
(Note: This isn’t intended to be a critique of the Broad Street Hockey article because the gist of the article is true. The premise of the article is really about statistics needing context and I agree with this 100%. I just wish it wasn’t limited to stats like plus/minus, turnovers, blocked shots, etc. because advanced statistics are just as likely to be misused.)