It isn't public knowledge anymore, but in the past Harrah's let you see some of this data online. And at that time they seemed to focus on 3 ADT numbers based on: your last 6 visits, the last year, and the last 2 years. They easily may have changed this method by now, but it's probably a good starting point.
More details can be found here:
I have also heard that CET has a complex formula that comes up with a final number to determine how much you are "worth" to them. In this formula, I would assume ADT is the biggest factor, but if two players have an ADT of $1000 and one of them shows up 3x more often to play, he or she would be more valuable, obv.