Posted by Neil on October 10, 2013
In case you missed it yesterday, we rolled out a couple of new goaltending stats for the 2014 season -- Save Percentage+ and Goals Saved Above Average. Overnight we got some feedback about SV%+ in particular, and the structure of having 1 minus the goalie's own SV% in the denominator of the formula. Right now, we are measuring the rate at which the league allowed more goals than the player, where 100 = average. So in the case of a 133 SV%+, the league's rate of goals allowed per shot would be 33% higher than the player's rate.
There are other alternatives. If we re-arrange the formula so that 1 minus the league SV% is in the denominator, we would be measuring the rate at which the player allowed fewer goals than the league. (Because of the nature of division, this is an important distinction from the definition in the previous paragraph.) If we tweak the formula in this direction, there are 2 options: we can compute a "minus" type of stat in which lower numbers are better, or we can stick with the "plus" style familiar to all from baseball's OPS+ and ERA+. The former would represent a goalie who allows 33% fewer goals than the league as a 67 (remember, lower is better); the latter would represent that as a 133.
As is the case sometimes in this business, there is no "right answer" here, but rather a matter of preference. For instance, we've long assumed users would find it counterintuitive to have a rate stat where lower numbers = better performance, but maybe that's not true. I'm interested in opinions on this, so let your voice be heard in the following poll -- which format do you prefer? Or do you care at all? I can't promise the poll-winning format will be what we eventually stick with, but I'd like to know what people think.