Rather than looking at raw Sv% and adjSv%, we can instead look at
Goals Saved Above Average (GSAA) which attempts to measure how many extra goals a given netminder prevented over a league-average goalie:
GSAA = (Sv% – lgSv%) * SA
most goalies GSAA fall between -10 and +10,
GOALS SAVED METHOD
The idea is to come up with a team independent measure of how many goals a particular goalie saved (when compared to an “average” goalie).The idea is to find the extra number of saves a goalie makes when compared to “average”
SUCCESSES OF THE GOALS SAVED METHOD
This method attempts to come up with a single number to score goaltenders - which represents the number of extra goals the goalie saved over the average goalie that season playing for the average team.
Any goaltender who has a Vezina Trophy calibre season (using the modern day voted Vezina - until 1981 the Vezina was won by the goalie(s) on the team with the best goals against average) should be at (or at least near) the top of the league in goals saved. Usually this is true, but sometimes it is not. This method is very good at isolating those goalies.
Correct more then 2/3 of the time in predicting the Vezina winner
FAILURES OF GOALS SAVED METHOD
This method is very successful in picking the best goalie in a given season but has problems when comparing between different seasons. This is because the comparison to the average goalie in a given season has no meaningful carry-over from one season to the next.
A further problem occurs because shot quality data is not taken into account (it does not exist before 2002/03). Thus teams with top defences that allow lower quality shots will appear to have better goalies.
GSAA – ESSENTIAL TO EVALUATE GOALIES
(Feb 19, 2014)
“GSAA” – Goals Saved Above Average. You take the league’s average save percentage and apply it to the amount of shots a particular goalie has faced. You get a number of goals that the average goalie in that league would have surrendered if they faced the same number of shots as the goaltender in question. That number gets compared to the number of goals surrendered by that goaltender, and a plus/minus is created. If a goalie is in the positive, that is how many goals they have saved compared to a league-average goalie. If they are in the negative, then it is safe to assume that they are performing worse than how a league-average goaltender would perform in the same situation.
RYAN MILLER
GSAA creates a direct comparison to league average, as opposed to a stand-alone percentage.
With GSAA, the assumption at a glance is that the goaltender in question is performing better or worse in comparison to the league average that season. It is a hard and fast number. And that’s nice.
GSAA is as good of a “result-based” stat as is available out there for comparing goaltenders against their peers, season over season.
As it stands, GSAA tends to favor goalies who have a larger body of work. Because saves are cumulative and saves are a part of the formula, it makes sense that the more saves you have, the less likely a league average goalie can match your performance over the long haul.
adjGSAA/60
adjGSAA/60’s purpose as a tool is a baseline comparison that makes it easier to look at a list of goalies and determine as definitively as possible, regardless of circumstance, and in consideration of the tools we have and the variables we can actually account for, Goalie A is performing better than Goalie B.
NHL goaltenders do not compete on a level playing field: In any given game, some goaltenders face many difficult, close-range shots, while others face many easy, long-range shots. To account for this, we use “Adjusted Save Percentage”, which takes into account the ‘quality’ of each shot they face based on the empirical league-wide shooting percentage from that area of the ice.
The solution is to incorporate weighting by danger zone.
The resulting stat, 5v5 adjGSAA/60, thus gives us a much better picture of how much better, or worse, the goalie in question has done than an average goalie would have, had he faced the same danger zone workload.
5v5 adjGSAA/60 is a great way to easily compare goalies much more concretely than sv% alone can.
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