Every year I get a few requests from players regarding the GAA calculation with the stats tracker. Most ask “Why is my goalies GAA 2.667 for the game when he only had 2 goals scored against in the 45 minute game?”
The reason is pretty simple: GAA = 60 * (GA / Minutes Played)
Goalie Analytics Season GAA Trend
The definition of GAA is to average the goals per min and then multiply by 60, so that it is a comparable average to a standard 60 minute game. This way you can compare your goaltender performance to other goaltenders (such as college, NHL, or whatever). I know my players like it when then can compare their GAA vs. the top NHL goaltenders, etc.
What some ask for is really a goals per 45 min game average, which would only make sense to compare against goaltenders that play the same duration of games.
To answer the concern is that a goaltender only lets in 2 goals during a 45 minute game and ends up with a 2.677 GAA for that game. That is basically how it works. Had that goaltender played an official 60 minute game, it is likely on average that would be the number of goals that would be allowed. Things can be further complicated when teams go to tournaments and play 3x 10 min stop time or any variation.
This calculation is the same as ERA for pitchers – if a pitcher has 1 earned run and only pitches 1 inning, the ERA is 9.
For comparing many performance indicators in hockey, school, and any number of examples we use the percentage. Percent is parts per 100. For a younger child in school we don’t try to color results by justifying 7 out of 8 on a test score (which is 100*(7/8) = 87.5 percent) as being 70 perocto (which is 80*(7/8)) – that just would not make sense because it is not a common way of looking at school test scores, (even though they are young kids and they never see tests with 100 questions on them, they are usually only 80 questions).
My point is that it will be more useful to stick to standards. Also, keep in mind that GAA is just one statistic. There are many areas of performance that should be considered to measure a goalies performance, such as rebounds allowed, save percentage for differing shots and from differing ice locations. If the GAA number is concerning, focus on Save Percentage. That can’t be misinterpreted and is more representative as the goaltender’s individual performance.
With that being said, we have released a new product for advanced goalie statistics and analytics. Within that product we do provide the standard GAA for a 60 minute game, and the GAA-G based on regulation duration of each game (which can vary). It is a more complex calculation and really becomes a large weighted average across all games of varying length, but it provides one more piece of information to consider.
Season Summary Stats with GAA-G
Above all, statistics are not an answer, but information to help you think about performance. What is good, what can improve, and what is that stat telling us?
The focus in our hockey stats products is to capture as much data as possible and provide it in forms for you to analyze and interpret easily. For example, our Goalie Analytics product for Microsoft Excel provides goaltender performance visualization by using the magic quadrant presentation. Below we visualize Rebound Control vs Save Percentage by Originating Shot Location and display the significance of each shot location by it’s bubble size which is the number of shots faced from that location.
The magic quadrant is the upper right hand corner as you can’t get much better than that. You can easily see with one visualization that Goalie 2 can improve rebound control for shots that originate from the left hand side of the slot. The second chart above shows the Shot Location Analysis which indicates the shot height in inches off the ice, and the shot distance in feet from the net.
You can learn more about these products at Colorado Hockey Institute, and thanks for asking the questions.
Founder, Colorado Hockey Institute