There's a number of factors that can effect your eCPM, like mentioned the geo makeup of your traffic. If you have all Chinese and Indian traffic that will effect it.
Also, what type of banner and where was placed your site? If you are using some weird size banner buried deep in your page that most advertisers aren't interested in, it will still get the impressions but not a good eCPM.
If you would like for me to look into your account specifically and see what can be done to improve it, hit me up as I'm always glad to help, and as you can see from other replies we do work well for many people.
