Defining key performance indicators for things like these is not very hard, neither is developing ways to measure the performance. Tweaking the accuracy and fixing the gamable parts once the basics are done is the harder part. Also these metrics should like any theory be in a continual beta state and get tweaked, just make clear that the trend compared to previous measurements is broken. I can spend a little time on irc teaching someone how to do this but my time is extremely limited right now so it will have to be a formalish appointment with an eager student.