joined:Dec 30, 2008
For some time I had two 330x250 ads with the same code and the same channel, but because I wanted to serve ads with DFP (double click for publishers, former ad manager), I separated these ads, creating two separate channels.
The very same day my CTR plummeted, eCPM plummeted but number of page impressions increased. However Google Analytics showed the same number of visits.
Before this change I was under impression that it doesn't matter how many ads and channels you have on the page in calculation of page impressions, but it now seems to me that Page Impressions shown on the report overview is Ad Impression.
For example, we have one page with 3 ad units and for some period of time we got 100 visitors and each of them clicked one of these 3 ads. You would expect CTR 100%, but in AdSense reports in will be just 33% (100 clicks with 300 page impressions).
As can be seen from the example above, this number negatively affects both CTR and eCPM, and makes it impossible to experiment with CTR on a single site let alone compare CTR and eCPM of different sites even in the same niche. And I won't be surprised if these data is available to advertisers if channels are targetable, so probably affects website earnings in a negative way as well.
The question is - is this possible to do anything about this except changing everything back?