I am not 100% versed as far as this topic goes. But what I can gather so far from CPM, is that it has a lot to do with where your page views are coming from. For example you may get higher CPM, from google viewers than from hubpage viewers. Also the help forum, is a great place to post additional questions in reference to this topic. In addition to this-view the learning section of hubpages-this is also a great resourse. Good luck with your writing.