Anyone who has followed this blog for a while knows that I dislike arguments based on the number of games played by a goalie. If two goalies have a similar level of performance and one has played substantially more games, then it makes sense to take the guy who has more games played because it less likely that his performance was simply a hot streak or a good run of luck. However, often a goalie who has easily outplayed another goalie is considered inferior because he played less games, even though he would have had to play horribly in the remaining games to drop down to the other goalie's level.
Is there a big difference between a goalie who plays 50 games and a goalie who plays 65? Most people probably would say yes, and I know that most award voters would agree with that statement. The problem is that I doubt any of them ever tried to quantify the difference. What if the 50 game guy has a .935 save percentage, and the 65 game guy has a .905 save percentage? What about .925/.915?
I haven't seen any evidence that there is a statistical difference between playing 65 and playing 50 in terms of fatigue affecting your play. Fifty also represents the bulk of the season, which means that the additional games played do not have a major effect on the average.
To demonstrate this, let's take a goalie who has played 50 games at a pretty average level on an average team (say, .908 save percentage), and consider two scenarios, Scenario A: He plays the last 15 games like the best goalie in the league (.940), and Scenario B: He plays the last 15 games like the worst goalie in the league (.880). What is the effect on his seasonal numbers?
Scenario A: .915
Scenario B: .901
In both cases, his seasonal save percentage moves just .007, even though the extra 15 games played were either fantastic or horrific. It is pretty unlikely that NHL goalies will put together results more extreme than either of those two over a 15 game stretch.
Do the same thing comparing 50 games to 75 games (adjusting the save percentage assumptions a little closer to say, .930 for A and .890 for B since the games played sample is larger and extreme results are less likely to occur), and we get a split of about +/- .010 in save percentage.
I think that is a safe general rule of thumb to use, that if one goalie is .010 or better than another in save percentage, after adjusting for the team context they play in, and if both goalies have played the majority of games for their teams and you don't suspect there is any large differential in shot prevention between the two, then you can pretty safely say that the goalie with the higher save percentage is better. Even if one has played 70 games and the other has played 50.
Let's do a similar calculation for Tim Thomas this season to show that he was demonstrably better than the two other nominees, even though they played more minutes. Thomas played 829 fewer minutes than Backstrom, and 405 fewer minutes than Mason. If we assume that Thomas would face the same shot rate against if we has to play those extra minutes, we can figure out what stats he would need in that extra playing time to match Backstrom's and Mason's numbers.
To match Backstrom: 3.26 GAA, .884 save %
To match Mason: 3.85 GAA, .778 save %
Tim Thomas this season: 2.10 GAA, .933 save %
Tim Thomas, career: 2.62 GAA, .918 save %
How's this for a stat: If Tim Thomas played in 11 extra games and faced his usual shot rate, he could have allowed 5 goals against and lost every single one of them, and he still would have a better winning percentage and save percentage than Steve Mason.
Decide for yourself how likely it is that fatigue or any other factor involved would drop Thomas below those other guys.
Those are unadjusted numbers, of course, so take that into account. Shot quality measures suggest that Thomas faced tougher shots than Backstrom, but easier shots than Mason. We can calculate the shot quality factors that would be necessary for Thomas to have equivalent performance:
To match Backstrom: Bruins 13% easier SQA than Wild
To match Mason: Bruins 20% easier SQA than Blue Jackets
The typical spread from best to worst in the entire league is about 20%, so to argue that Mason's team-adjusted performance was better than Thomas' you would have to demonstrate that Boston was the best team in the league at shutting down opposing scoring chances, while Columbus was the worst. Even then the two of them would be virtually tied, so it would be a coinflip as to who wins.
Tim Thomas should win the 2009 Vezina Trophy. He should also be the First Team All-Star. I'm pretty confident Thomas takes the Vezina, as I don't even see the argument for either Backstrom or Mason to finish ahead of him, but I'll be interested to see what the writers do. They tend to put more weighting on things like wins and games played, so they might throw everyone for a loop and go with Mason, or even Evgeni Nabokov again.