Interest based ads is the reason, I am sure, my earnings are all over the map recently. My ctr has tanked on many days, making it more difficult to earn a steady daily revenue as I have for years now. I can back this up with my own experience.
Nine days ago I was searching on the web for a product that is so rare, I would bet not a single WW user would want, need or seek one. The reason I was searching on the web is because the product is so rare I couldn't find it in my town, any town nearby and none of the local companies who might have sold it if it wasn't so rare couldn't find one from their wholesalers so they could sell it to me either. After they had given me the run-around for a week or so, I decided to try to find one myself on the web last Monday. This was not a luxury item, I NEEDED it desperately. So, I hit the web, found one, had it shipped to me, it arrived last Wednesday and I am currently using it. The item arrived within two days of ordering it. (God I love the web!) I bought the item through a company I found in Google search listings, not the company who was advertising heavily on the search results page. That was because the Adwords advertiser's product was going to be shipped from a site that was UPS Ground zone 5 to me. I found a supplier who was clearly zone 2 to me, meaning I could get it quicker, and shipping was free.
Every day since, including as recent as ten minutes ago, I am seeing all three Adsense blocks on any of my own sites, showing me ads for that product I searched for. Not a single site I own has any content, not a single word, that would pull those kind of ads. If I was seeing those ads on your site and you were showing ads for SHOES, the odds of me clicking on one of those ads is nil. I am shopping for shoes now, not this obscure, one in a million product that has nothing to do with fashion, women, clothing, shoes or accessories. I have bought the product and in fact, will NEVER buy the product again. I will never need the product again. Yet, for at nine days and counting, I keep getting ads for that product.
I can think of other products this might happen with. Let's say today you are looking for an attorney to handle a wrongful dismissal at your job. You search for one, hire one and then go on with your life. You land on my site that has information on buying cockroaches (I don't have such a site). When you land on my pages instead of seeing ads for cockroach suppliers you see ads for employment attorneys. What are the odds at that point that you will click on my ads? Nil.
While the broader concept of interest based advertising seems valid, in real life practice there are countless instances where showing ads based on what I was interested yesterday is in no way an indicator of what interests me today, or any day in the future. If my interest is based on a cookie, the cookie time frame needs to be reduced to a couple days at most. Otherwise, publishers and Google as a whole are going to see a decline in ctr and revenue.
My channels are broken down by topic. Each topic has a maximum of 10 pages, so each channels is very finely tuned. I can see exactly what is going on any of my sites and have been tracking statistics for over eleven years, six years with Adsense. I know my visitors. Because the recent ctr was so insane, I knew the only answer had to be untargeted ads. I went out to research it and in the course of doing that, figure it based on my own personal experience. If I am seeing highly untargeted ads, what are my visitors seeing? Untargeted ads. I don't think there is any other logical answer. Interest based ads are killing my income.