Wednesday, April 22, 2015

Are Swedish Goalies Overvalued?

In doing the research for my post on Jacob Markstrom, one of the things I did was run the numbers for all Swedish goalies who have played in the NHL over the past 25 years.  That chart didn't end up making the final cut, but it was interesting enough on its own that I want to post it in here in the context of a discussion on the recent performance of Swedish goalies in the NHL and what that might be able to tell us about the effectiveness of that country's goalie development model.

Here is the complete NHL performance of every goalie from Sweden since 1990, with league-average adjusted save percentages normalized to .914:

Two things stand out from that chart:

1. Sweden has really blossomed as a goalie producing country over the last decade (15 of the 23 Swedish goalies to ever play in the league have made their debut since the 2005 lockout).

2. The save percentage numbers are quite mediocre for the group as a whole, with the exception of the outstanding Henrik Lundqvist.

Wednesday, April 15, 2015

Predicting Playoff Success

From Alan Ryder's Ten Laws of Hockey Analytics:
One important warning - do not confuse correlation with causation.  The former is easy to prove, the latter is quite challenging.  For example, carry-in zone entries yield more scoring chances than do dump-in zone entries.  But this could mean that a carry-in is evidence of better neutral zone puck control rather than a cause of better offensive zone puck control.
Which of these variables do you think is the best predictor of playoff series winners in the NHL between 1984 and 1990?  In other words, if you were betting on matchups back then and could only look up one stat for each team to influence your decision, which is the one that would most frequently point to the eventual victor?
  1. Goals For
  2. Goals Against
  3. Shot Differential
  4. Team Shooting Percentage
  5. Ratio of Shorthanded Goals For vs. Against
It's gotta be #3, right, based on what we know about the importance of possession?  Or maybe #1 or #4, since offence had to be important in a league that was wide open and high-scoring?  Or perhaps that old saw about defence winning championships held true, and it was really #2?  The one that seems most out of place is #5, a variable measuring rare events that doesn't take into account anything that happens during the game's most frequent and important game situation (even strength).

But if we look at the numbers after the jump, we get some surprising results:

Thursday, April 9, 2015

Arbitrary Endpoints, Career Numbers, and the Future of Jacob Markstrom

(As an introductory note, it's been a while since I posted here, but a lot has happened in the interim, not just on the ice during the 2014-15 season but especially off of it, with the Summer of Analytics, the emergence of new statistical resources, and some interesting perspectives on goaltending from Steve Valiquette, Chris Boyle, and others. On top of all that, I was also inspired by attending the Ottawa Analytics Conference and meeting many of the people I have worked with and interacted with online.  All that means I'm planning to get back into hockey analytics, which for the time being will include contributing to the Hockey Prospectus Annual and blogging in this space.  Although I was pretty fortunate in having my last post here be on a topic that makes me look pretty good in hindsight (Dubnyk vs. Scrivens), it's long past time to starting pushing that one down the page.)

One of the things I have been thinking about lately, and something I wanted to bring up in my first post back, is the issue of career stats and arbitrary endpoints, to borrow a term used by ESPN sabermetrician Keith Law.  Here's the description from Law's glossary:
#arbitraryendpoints: Also known as cherry-picking, this means choosing one or both endpoints on a series of games to try to analyze a player. I’ve argued that it’s not arbitrary if the endpoint is tied to something specific, like a change in mechanics, an injury, or a recall from the minors, but even so, it’s always dangerous to throw out any data when you want to draw a conclusion.
I definitely agree that it is dangerous to throw out data and that it should never be done for the purposes of supporting an already-reached conclusion.  However, I also agree that it is not always arbitrary to look at splits and segments of data rather than relying on the complete sample if there is good reason to expect that some of the data is not representative of an athlete's true talent level.

There seems to be an increasing trend on Hockey Twitter for people to simply pull up a goalie's career save percentage or career EV SV% and use that as the final verdict on their talent level.  This can certainly be appropriate some of the time, perhaps even most of the time.  I still think that goaltending is above all else a results business, and that statistical measurements remain very powerful methods of evaluating performance.  That's why save percentage over a large sample size is usually a good proxy for a goalie's talent level.  However it is still only a proxy, and the three points mentioned by Law do also apply to goaltenders.  In the same way that Law might discount a pitcher's performance in his first year back from an arm injury, we might have reason to believe that a goalie could be deviating from his historical average because he is not yet at 100% health after coming back from some time off or has made some changes in his game after working with a new goalie coach.

On top of those factors there are others more specific to hockey goalies, such as team effects/shot quality, situational performance (e.g. EV vs. PK), home scorer bias/road performance, usage, etc.  These factors generally do not have a major impact on stats, but margins are so slim in goaltending that even a slight advantage or disadvantage can have an effect on the rankings.  Overall, I think sometimes insight can be missed by looking only at the big picture, and in those cases it is appropriate to take a deeper look.  And I'll start doing that by focusing a magnifying glass on the short but interesting pro career of Jacob Markstrom.