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I am not sure if it is the case for Adsense, however I do see when serving 3 blocks with the same units. For exmaple 1 leadboard => 2 half banners and 1 full banners, will reduce the CTR, then the PPC is also lowered.
Does anyone (especially for busy sites or for Fedex club members) find this as well?
I tested this twice. It confirmed twice, so I changed the format back to 1 block of leadboard each time after 3-7 days.
By the way, my CTR and PPC are very stable. Almost exactly the same every day. Impressions are in good numbers. So I would say I have a good sample to compare with.
Let's say there are 8 advertisers paying
$8 $7 .. $1 per click
I put a banner - 2 units, so the $6-$8 are rotating for the top2 slots.
I got 2000 impressions, so I burned 4000 unit impressions, and got no clicks. Adwords will put Disabled on the top 4 advertisers. What will they do? Paying more per click? Chaning keyword? Lower payment, or Withdraw?
1 Paying more means they are qualified for more impressions and low CTR before being disabled
2 Paying less means they can enjoy lower position for lowered CPM cutoff
3 Changing keywords means they will move to less generic words, where competion is lower so they can rank high with less payment, or it may also mean the few publisher will enjoy the high EPC.
I got 2000 impressions, so I burned 4000 unit impressions, and got no clicks. Adwords will put Disabled on the top 4 advertisers.
Adwords will never disable these ads based on the results from the content sites.
One time I had an ad-group with over 100,000 impressions a day from content match and CTR of 0.01% for a week. All these did not effect my ad.