After the introduction of SV%+ to goalie stats a little over a week ago, there was some discussion as to whether or not it was the best way to represent goals allowed relative to league average. After reviewing some poll results, we've decided to change things up a bit and switch the representation to Goals Allowed %- (the minus because lower is better). The formula is now 100*((1-player save %)/(1-league average save %)) -- this means that Semyon Varlamov, who currently has the best save percentage in the league at .965 (vs. league average of about .913), gets a 40 GA%- &emdash; on a per-shot basis, he allows goals at 40% of the league average rate. Conversely, Martin Biron has allowed 9 goals on 38 shots, which gives him a GA%- of 273 (yikes). This works out better for us because goalies who have not allowed a goal will get a 0 GA%- instead of getting an undefined value as they would have in the old system.
In case you missed it yesterday, we rolled out a couple of new goaltending stats for the 2014 season -- Save Percentage+ and Goals Saved Above Average. Overnight we got some feedback about SV%+ in particular, and the structure of having 1 minus the goalie's own SV% in the denominator of the formula. Right now, we are measuring the rate at which the league allowed more goals than the player, where 100 = average. So in the case of a 133 SV%+, the league's rate of goals allowed per shot would be 33% higher than the player's rate.
There are other alternatives. If we re-arrange the formula so that 1 minus the league SV% is in the denominator, we would be measuring the rate at which the player allowed fewer goals than the league. (Because of the nature of division, this is an important distinction from the definition in the previous paragraph.) If we tweak the formula in this direction, there are 2 options: we can compute a "minus" type of stat in which lower numbers are better, or we can stick with the "plus" style familiar to all from baseball's OPS+ and ERA+. The former would represent a goalie who allows 33% fewer goals than the league as a 67 (remember, lower is better); the latter would represent that as a 133.
As is the case sometimes in this business, there is no "right answer" here, but rather a matter of preference. For instance, we've long assumed users would find it counterintuitive to have a rate stat where lower numbers = better performance, but maybe that's not true. I'm interested in opinions on this, so let your voice be heard in the following poll -- which format do you prefer? Or do you care at all? I can't promise the poll-winning format will be what we eventually stick with, but I'd like to know what people think.
Today on Hockey Reference we're rolling out two new stats for goalie pages: Adjusted Save Percentage (SV%+) and Goals Saved Above Average (GSAA). First, you can check Broad Street Hockey for a great explanation of adjusted save percentage and goals saved, but for a simple look, consider the 2012-13 NHL season. League-wide, there were 41,827 shots overall and 3,684 goals scored, for a goals against average of 8.81%. Vezina Trophy winner Sergei Bobrovsky had a goals against average of 6.87% -- 29% better than league average, giving him a SV%+ of 129. Taking that 29% better performance into account combined with the number of shots he faced, we say he saved 21.48 goals more than an average goalie would have, given equal playing time.
These stats are especially helpful for comparing goalies across eras: Patrick Roy led the league in save percentage in the 1991-92 season with a .914 SV%; in the 2012-2013 season that would have placed him as the 26th best goalie between Ben Scrivens and Jonas Hiller. However, we can look at his SV%+ of 130 for that year and see that he was actually 30% better than the league average at stopping goals -- better than Bobrovsky, even.
Note that SV%+ has a minimum requirement of 4 shots faced per team game, so that we don't have goalies who stopped 7 of 7 shots faced in their single period played skewing the results. These stats are now up for goalies as far back as the 1983-84 season (the first year we have shots against data for the NHL), and for the entirety of the WHA (1972-1979), and will be updated throughout the year.
I am sad to announce that after six years, five websites, and hundreds of thousands of lines of code, my tenure at Sports Reference will come to an end this week. More information can be found on my new blog, Statitudes. Thanks to all of the users who have supported the sites that I ran.
Every Monday, for the rest of the year, we'll be randomly selecting one twitter user who follows any three of our five Sports Reference Twitter accounts to receive a free Baseball-Reference.com Play Index account. If you are already a subscriber, we'll extend you for a year.
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In preparation for the NHL Playoffs dropping the puck tonight, we've added preview pages for each series matchup to the front page. There, you'll find season stats for all the players currently on each team, plus the season series results between the two teams, and various other vitals. Have them open on your computer or print them out while you're watching the games tonight.
In anticipation of the NHL playoffs, we've updated the front page for the postseason. In addition, we've added playoff matchup pages for each series, where you can see how two teams stack up against each other at a glance. These pages have listings of how the two teams fared in regular-season meetings this year (plus a link to see how they've played each other all-time) and the current series status.