Difference in page views count for different ad networks

[neku]

I am using multiple ad networks on some websites to maximize the revenues from the few websites getting traffic.. I have noticed that some ad networks are showing more than 3000 page views daily, while others are showing 400 page views for the same domains. What could be the reason for the difference in page views?

 

[Nomad]

Some ad networks count unique views only where as some ad networks count all views. Some ad networks even count bot views where as some ad networks do not count bot views. That's why the difference exist.