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Stefan Frei has been impressive this season, making save after save in key moments to keep the Sounders in games on multiple occasions. Unfortunately, he apparently didn't do enough to impress voters and isn't a finalist for the MLS Goalkeeper of the Year award. The finalists named by MLS are Bill Hamid, David Ousted, and Luis Robles.
It should be noted that goalkeeper statistics are not very advanced and don't tell us a whole lot. Depending on the style of the goalkeeper and that of the team he plays for, goalkeeper statistics can make a mediocre GK look a lot better than he really is or make a great GK look less great. It's obviously better to have a higher save percentage than a lower one, but that can be influenced by how good a player is at organizing his defense. The GK who isn't as good at that might face more weak shots that might have never occurred if the defender or even the GK had been in better position.
The problem is that there really aren't a ton of alternatives available to compare goalkeepers for things like the MLS Goalkeeper of the Year award. That being said, this is where the finalists for MLS Goalkeeper of the Year award finished in 2015 statistical categories, compared to Frei:
Bill Hamid
1.16 GAA (6th)
75.9% save rate (2nd)
133 shots faced (8th)
101 saves (5th)
0.76 open play GAA (8th)
0.32 clean sheets per game (tied for 6th)
David Ousted
1.06 GAA (tied for 2nd)
72.3% save rate (4th)
137 shots faced (7th)
99 saves (6th)
0.71 open play GAA (5th)
0.38 clean sheets per game (2nd)
Luis Robles
1.26 GAA (9th)
65.6% save rate (11th)
131 shots faced (9th)
86 saves (10th)
0.74 open play GAA (tied for 7th)
0.26 clean sheets per game (tied for 9th)
Stefan Frei
1.06 GAA (tied for 2nd)
77.1% save rate (1st)
144 shots faced (4th)
111 saves (3rd)
0.68 open play GAA (2nd)
0.32 clean sheets per game (tied for 6th)