I have done a bit of research into the Original Six lately, which has become a point of interest for me because of the close relationship between team strength and goalie stats in that very unbalanced league. I mentioned before that goalies on the best teams never had to play against their own Hall of Fame shooters. Here is a some evidence that proves this point. From 1946-47 to 1955-56, Toronto, Montreal and Detroit were the three best defensive teams almost every single season. That makes it easy to divide the league in two with a strong group and a weak group. I looked at the results of games when the strong teams played the weak teams, and here are the goals against averages for each team against the Bruins, Hawks and Rangers combined:
1. Detroit 2.22
2. Montreal 2.22
3. Toronto 2.25
That is stunningly similar for a 10 year sample size. Based on those results, I think it is reasonable to conclude that the overall goal prevention ability of each of those three teams (team defence and goaltending combined) was roughly equal. Here's how they did against each other:
1. Detroit 2.15
2. Montreal 2.30
3. Toronto 2.44
As we can see, the overall difference between the teams came entirely from their results against each other. Now we don't have save percentages for those seasons, and we can't necessarily rule out the possibility that, say, Detroit's defence was worse than Toronto's but they made up for it with superior goaltending. Still, it makes one wonder whether Terry Sawchuk's biggest advantage was really his goaltending skill, or merely his good fortune to avoid having Gordie Howe and Ted Lindsay spoil his shutout bids.
This is certainly something to keep in mind for older goalies, but a similar effect can still show up in more recent years as well whenever there is a single dominant team in the league, or a few teams that are a level above everyone else. A goalie on a great team often has great playoff stats because he never had to face his own team. It is also a potential flaw with using playoff results adjusted compared to league average. Grant Fuhr's league-adjusted playoff stats, for instance, probably look relatively better than they should since his Oilers were out there wrecking everyone else's. I bet Fuhr's numbers would be a lot closer to average if I took out all of the playoff games involving Gretzky's Oilers and then recalculated the year-by-year league averages. I'd like to see a similar calculation for guys like Billy Smith or Chris Osgood as well.