Here is the situation: I have a well-performing adsense ad for a long time, located at the bottom of each page; it associated with channel named "Bottom". Month ago I've added one more ad to the pages, it is located in the middle and have corresponding channel - "Middle". Formats of these ad blocks are the same. Now looking at the stats I see that my "old" bottom block have two times higher CPC than "young" middle block. On the other hand, "Middle" has much higher CTR (because it is located higher and more integrated with content). So the question is: what factors can affect CPC (position, channel, CTR)? Is it possible that Google has "ad block performance history" assigned with some channel or some unique ad-block-defining parameter, which can affect CPC?
I thought ads were placed depending on the order in which the ad code appears in the HTML. Did you put your bottom ad with a DIV? Is it before or after the middle ad?
No, no CSSed DIVs, all ads appear exactly as they are inserted in HTML. I.e. javascript code for "Middle" resides higher than "Bottom" code in the page HTML. "Middle" ads appear earlier in code but have lower CPC.
no, the first ads that show up in the code are ranked there because of: 1)the likelyhood that they will clicked on 2)their adwords bid was higher so the mfa pond scum, with their deceptive ad text, may rank higher in the ad blocks because google thinks that they will get more clicks than an ad that pays more.