There was an interesting exchange over at Battle of Alberta today:
Cosh: Is there actual evidence that there is any point in breaking overall save percentages into smaller, noisier samples? Or is this just cargo-cult sabermetrics (it works in baseball, so…)?
After some further discussion that included, of course, a reference to Roy Halladay’s fine record against the Yankees this year, Fenwick kicked out the following:
Matt: In 06/07, two goalies had >.900 PKSV%. Their overall save percentages, between that season and this past one, dropped 27 and 9 points. Is that the same as parsing this fellow Halladay’s record for little slices that aren’t likely to be repeated? I don’t think it is, but again, I don’t know what it is you want to see.
This intrigued me, for a number of reasons. First of all, because it suggests a simple rule, a line in the sand. “Goalies who have big PPSV% seasons can expect their overall save percentage to fall in the following season.” We can’t call this a Fenwick number, for obvious reasons, but the principle needs something to go by and doctrines seem popular at the moment, so the Lethbridge Doctrine it is.
How does the Lethbridge Doctrine hold up? Fairly well, I think. Before I go to my results, let me explain how I did it. As everyone knows, the NHL save percentage has moved over time. This is the function of a couple of things: first, generally, fewer pucks have been going into the net and, more subtly, the percentage of shots that are taken on the PP, which are much more likely to go in, has jumped around a lot, from a low of 17.4% in 1999-00 to a high of 24.8% in 2005-06. The goaltending data from 1998-99 to the present date looks like this:
So as to have a workable set of data that isn’t swayed by shifting save percentages, I scaled everything to a league in which the average save percentage was .907 and in which the splits were .917/.866/.916. I’ll call this a scaled save percentage. So as to limit the extent to which the data is altered by shifting proportions of ES/PP/PK shots, I also calculated save percentages for all of the goalies in this little study as if they saw 76.1% ES shots, 20.0% PP shots and 3.9% SH shots.
Next step was to define a group to look at. I just picked the top five from each year in PPSV% (minimum 200 PP shots faced) and compared their scaled save percentage from that season to their scaled save percentage the following season. The results are pretty interesting.
Of the forty goalie seasons that gave me, 33 of them put up worse scaled save percentages in the following season. The average decline was by 0.010 worth of save percentage. Every hundred shots, that’s a goal that wouldn’t have been given up the year before. That’s effectively an extra goal against every three or four games. Two stayed the same and five got better. 25 of them were at least 0.008 worse, which is a big dip.
What does it all mean? Well, based on the last eight years, you might reasonably argue that four of the five best PPSV% goalies in the NHL will suffer drops in their scaled save percentage this season. Who will be the five staring down this unfortunate history in the coming season? Martin Brodeur, Niklas Backstrom, Carey Price, Tomas Vokoun and…Mathieu Garon.
Garon actually carries a special burden into the coming season – he had the best PPSV% in the NHL in
2006-072007-08. Of the eight players to lead the NHL in PPSV% since 1998-99 who have already played their next season, the average decline in scaled save percentage was 0.017, although it’s kind of odd – Ed Belfour (02-03 PPSV% leader) and Henrik Lundqvist (05-06) had declines of .006 in scaled save percentage, Roberto Luongo (03-04) and Martin Brodeur (99-00) had declines of .008, Dominik Hasek (98-99) had a decline of .015, Jose Theodore (01-02) had a decline of .026, Chris Mason (06-07) had a decline of .032 and Manny Fernandez (00-01) had a decline of .033.
The better places on that list have some starrier names. If I was a betting man – and I’m not – my guess for Garon would be pretty close to league average, as opposed to last year, whereas his scaled save percentage for last year was .914. I have a hard time seeing how the Oilers make the playoffs with that, no matter what that knob/idiot Mirtle says.