Sunny Mehta pointed out a very good change to the Quality of Competition algorithm. Instead of using relative +/- (which includes just goals when a player is on or off the ice), it would be better if Qualcomp used the total shot volume while players were on the ice. Why? We already know that shot differential (aka Corsi) is a better predictor of future goal differential than goal differential itself is. Corsi also includes a much higher number of events than simple +/- does - approximately 25x.
The relationship between Qualcomp and Corsi Qualcomp is still very strong (the overall R^2 = 0.54), indicating that we were on the right track initially. You can see the results here - Brent Seabrook and Duncan Keith are #1 and #2. I've only done this for 5v5 for the 2009-10 season; because of the genius way I wrote my database code, I have to make the same changes nine times in order to get this in to the entire site, which I'll do eventually.
I think of all the NHL teams, people out there pay closest attention to the Oilers matchups (even when the team is awful), so perhaps someone can give an opinion as to whether the Corsi Qualcomp is an improvement over regular Qualcomp:
There are some rather significant differences - I'm interested to hear if this works out better.