When some goalies are in the net, fewer shots are taken by the other team. Although I was once skeptical of this effect, it has been shown to be pretty clear in the historical data. Martin Brodeur is a goalie who usually gets a lot of credit for his puckhandling and other skills that likely contribute to a reduced shots against total. There are, however, other goalies who are also very good at those skills.
I believe the goalie who might be the most overlooked in this aspect of goaltending is Ed Belfour. Having closely compared their shots against records, there is good evidence to suggest that Belfour's shot prevention effect may be every bit as large as Martin Brodeur's.
Belfour is a little easier to evaluate since he averaged fewer games per season and played on a number of different teams during his career. To do my comparative shots analysis, I usually look for goalies that had both substantial playing time with the study goalie as well as lots of minutes played on other teams. There are three goalies that fit these criteria that we can use to evaluate Belfour: Jeff Hackett, Roman Turek, and Marty Turco.
In this type of analysis, I prefer to take the average of yearly averages rather than simply calculate an average from the totals, because otherwise it skews the data when there are seasons with much higher or lower minutes played totals. Belfour played with Hackett from 1993-94 to 1996-97, and averaged 27.3 SA/60 per season, compared to 29.2 SA/60 for Hackett. That is a gap of about 2 shots per game. Over the rest of his career, Hackett tended to face more shots than his teammates, averaging about one extra shot per game against. That gives us an estimate for Belfour of about one shot per game saved.
Belfour played two seasons with Roman Turek in Dallas, and faced 0.5 fewer shots per game. Turek was pretty consistently about a half shot below his goalie teammates throughout the rest of his career, which again supports the one shot per game number.
In his two seasons playing with Marty Turco, Belfour was about a shot per game better than Turco, which is impressive since Turco has been half a shot per game better than his backups over the last few years (and Dallas has tended to bring in goalies who play a similar style, so Turco's effect might even greater when you consider he is being compared to guys like Johan Hedberg or Mike Smith). It could be that Turco had not yet developed his skills to the same extent early in his career, or that he learned a thing or two from Belfour that he was able to apply later on, or maybe there were some other variables that were influencing the shot numbers.
The results from all three goalies suggest that Belfour has a shots against effect of at least one shot per game. I did another piece of work where I compared how the backup goalies did while playing with a specific goalie and how they did on other teams. Ed Belfour faced 26.7 shots per game, compared to 27.9 for his backups. His backups had a weighted average of 28.4 on other teams, which suggests that although his defences were better than average at preventing shots, Belfour contributed to his team's shot prevention.
For the sake of comparison, Brodeur faced 25.4 shots per game compared to 26.1 for his backups, who had a weighted average of 28.5 shots per game on other teams. This shows that New Jersey had a significant defensive effect. Subtracting the differences between the two of them, and you get a 1.2 shot differential for Belfour and a 0.7 difference for Brodeur. It is likely that weaker competition and other small sample size factors mean that Brodeur's figure is a bit understated, and those numbers do not include the 2008-09 season where Brodeur has so far faced about 2 fewer shots per game than his teammates. Still, it is more evidence that Belfour is comparable to Brodeur in terms of non-save skills.
I am willing for now to credit both Belfour and Brodeur with preventing 1 shot per game compared to average goalies. I also think that this information is the decisive factor that separates them both from other goalies like Joseph and Vanbiesbrouck who have similar save percentage records.
It does appear that the Brodeur vs. Belfour debate is a lot closer than most people would think. If these estimates are correct, then Brodeur doesn't gain an advantage over Belfour in terms of non-save skills, and the comparison between them should be decided by puckstopping ability alone. Brodeur has a better save percentage record compared to league average, but evidence suggests he also faced easier shots, since Belfour spent some of his career on bad teams (Florida, San Jose) and other parts of his career on teams that likely allowed shots of a higher-than-average difficulty (e.g. Toronto). If you compare Belfour's Dallas numbers to Brodeur's New Jersey numbers at the same time, which were likely two fairly similar team contexts to play in, their stats are essentially identical: 2.18 GAA and .909 save % for Brodeur vs. 2.19 GAA and .910 save % for Belfour.
I think that both have had pretty similar careers - they had some great individual seasons early, had lots of playoff and team success as members of terrific two-way defensive teams, and then spent a few seasons on weaker teams yet still performed pretty well. They also had some off-years mixed in, although New Jersey's defence did a better job of camouflaging Brodeur's down seasons compared to Belfour, who actually lost his starting job twice - to Hackett in Chicago and to Turco in Dallas.
The main reason that I think there is a reasonable case for Belfour over Brodeur right now is playoff performance, where in my estimation Belfour has been pretty clearly the better goalie. If my shot quality estimates in my last post were correct, then their regular season records might actually be pretty similar as well. Having said that, however, I think I would still take Brodeur's career over Belfour's right now, and with a few years left Brodeur will likely leave little doubt before his career is over.