I was wondering if there was any correlation between the amount of adsense content per page, and the CTR. (or similarily, the value of those added links) Recently, I added 1 or 2 more ad placements per page and noticed that my earnings went thru the toilet. Most pages have had only 1 placement. Just coincidence or is there more...?
My understanding is: If there are say 10 ads that match your site, and you have 4 ad spaces (a leaderboard 728x90 ad for example) then AdSense will pick the top 4 ads from the 10 possible and show them. If you have 12 ad spaces on your site, AdSense will show all 10, but the chances of your visitors clicking on the 4 top paying ads is now 4 in 10. This will cause a drop in CPM and Earnings, but should not cause a drop CTR, unless the site looks like it is too ad-orientated and people are just leaving or having so many ads makes them not blend as well as having a single ad. Switch back to 1 ad unit per page or blend them better, maybe try out different ad formats, or some link units.