Tried to search for an answer here but can't find one. Sure its been answered 100 times.... What determines how many ads are displayed in an ad block? Usually my block has 4 ads and the CTR is pretty good. Now there are just 2 most of the time and CTR is worse. What determines how many ads will be displayed?
Google would claim this ensures maximum earnings for your site. It's really all about odds. If there's a better chance, due to the ads and the click costs, depending on the specific visitor and where he came from, that displaying fewer ads in such a way has more chance of earning maximum bucks, then I believe that is what they do. Pete
Google has its own reasonings, but you can be safe in assuming that all of it is in the pursuit of more profits for itself, and as a result, for you. If two ads in a block keeps showing up, their algo has probably predicted that this will maximize earnings for your site. Why? I have no clue. Only Adsense knows, and it's not telling.
Could it have anything to do with the fact that some topics lack the number of advertisers to be displaying 4 in an Adblock all the time. I know that on my sites I tend to see much greater levels of ad block, and any format for that matter "full" of ads than on the sites with topics where I know the number of advertisers are limited... I don't know if this has any relation.
You could certainly investigate that by checking G search results to see how many advertisers there are- or even quicker with the AdWords or AdSense accelerator programs.
From my own experience it seems that my blocks are full, granted there are plenty of advertisers for the 'activating' keyword.