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What do we really know about Bob? (With charts and graphs!)

This is awesomely fantastic, so it's been bumped to the front. -- Travis

Bob's having a great year, no question. And he's just a rookie, so he should get even better -- have we found the next Dominik Hasek?

Not so fast. There's always variance -- some days things go a guy's way and some days they don't. And for goaltenders, that variance can take a long time to even out; it takes a lot more than a year to know a goalie's true talent level. Think about Tim Thomas, who has gone from great to an albatross to super-ultra-great in just a two-year span, and maybe you'll see what I mean.

My favorite metric for evaluating goaltenders is even strength save percentage (ESS%) -- it's kind of like save percentage, but looking only at 5-on-5 play. I prefer that to overall save percentage for two reasons: 1) Overall save percentage will make a goalie look worse if he's on a team that takes a lot of penalties, and 2) Power play shots take even longer for the variance to even out, since most of the game is played at even strength.

More after the jump. Charts! Graphs!

So let's think about Tim Thomas again. And to be fair, since he might be an extraordinary outlier, I'll include the guys right behind him on the ESS% leaderboard for this year: Niklas Backstrom and Ondrej Pavelec. Here's how they've done over the last few years -- look how much variance there is, and you'll understand why we don't know what we have in Bob after just part of a season.

Each of these goalies has -- in just a few-year span -- had seasons where they were better than Dominik Hasek's career numbers and seasons where they were worse than Roman Turek (or Andrew Raycroft or Patrick Lalime or a dozen other goalies at that level). That's why we can't just look at one season (or part of one season) and say how good a goalie is.

But averaging over multiple years does even things out a bit. Here's where those goalies' career stats were after each season (leaving out Pavelec because he got so little playing time his first two seasons so his numbers are screwy):

Not nearly as noisy, right? Neither of them has ever been near the Turek mark, and they've barely crossed the Turco line. There's still some fluctuation, of course, but now you feel pretty good about saying that both goalies are settling in as career .926ish talents.

OK, so you get the idea now, I like the ESS% metric but warn that it takes a couple of years of averaging to get a true talent level. So what can we say about Bob? Obviously we don't have a couple of years of data on him yet...but we do have some, so what do we know? This year, he's at .930 ESS%, which is below Hasek's career numbers but ahead of everyone else -- how much faith should we put in those results so far?

Let's start with a table -- here are all of the other goalies who meet two criteria: 1) their rookie season was 1998 or later, and 2) they had a ESS% of at least .925 in their rookie season.

Player

Year 1

Year 2

Year 3

Career

Sergei Bobrovsky

.930

 

 

 

Corey Crawford

.929

 

 

 

Jimmy Howard

.925

.918

 

.921

Pekka Rinne

.926

.925

.929

.927

Jonathan Quick

.926

.919

.927

.923

Steve Mason

.925

.911

.915

.917

Carey Price

.929

.920

.921

.925

Henrik Lundqvist

.929

.931

.922

.926

Kari Lehtonen

.927

.926

.925

.926

Andrew Raycroft

.941

.898

.914

.914

Evgeni Nabokov

.931

.929

.920

.924

Roberto Luongo

.930

.928

.925

.928

Martin Biron

.928

.905

.921

.920

Some things to notice:

1) Bob is having an epically good rookie campaign. Third-best of the last 13 years.

2) Aside from Pekka Rinne ticking up just a smidgin, all of these goalies have career numbers worse than their rookie season. Don't expect Bob to improve from where he is.

3) Aside from Andrew Raycroft, all of these goalies have all gone on to have very good careers. It's fair to expect Bob to be a starter for many years, and the only question is whether he'll be great or merely solid.

And one last plot, to explain why point 2 isn't just a statistical glitch. It's natural to think "shouldn't this fall on a bell curve, with some doing better and some doing worse?" But that's not quite right -- what falls on a bell curve isn't the list of very good goaltenders, but the talent of all goaltenders. 

Think about how steep that dropoff is in the tail of the distribution -- how rare a .930 career goaltender is. Think about how much random variance we saw from year to year in my first plot. Combining those, it should be clear why it's more likely that a guy with a .930 rookie season is a good goalie having a lucky first season than that he's a true .930 talent.

At this point, it's fair to expect good things from Bob, but whether he's great...that remains to be seen.

This item was written by a member of this community and is not necessarily endorsed by <em>Broad Street Hockey</em>.

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