Strange ECPM's

Just notice something strange, I have 2 sites with adwords on, one gets around 2000 ad impressions per day, the other gets about 100, both sites have the same content type, therefore the same ads appear.

The 2000 one has many more clicks than the 100 one, but the ecpm of the 100 one is usually 10x the other one....

Any idea why this is ?

Thanks

Subtle differences in the layout/location of the ads, or subtle differences in the content, netting a different kind of visitor. That's my $.02, anyway.

Same clicks on same ads tho ?

The one with 10 times less visitors is a 10 times higher ecpm ?

Any ideas ?

Are your audiences identical, down to the IP address?

Are the pages from the two sites ranked identically for identical terms?

Are your layouts and positioning identical, down to the pixel?

Nope, all am saying is that a click on a 100 impression a day site seems to be worth 10 times a click on a site with 1000 impressions.... not sure why.

How does the CTR compare between the two sites?