Below are 3+ things I had experienced with my Adsense account since 3 years.
1.Placing infolinks with adsense: when i used infolinks with adsense on my website my i have founded lot of different on my earnings.
2. Adding pop up social plugin: recently i place Facebook page promoter light box plugin on WordPress site that loads every time visitor visit the page on first page view. at this time user confuse close the popup scroll down for the content to eagerly to get it out instead of looking of adsense Layouts. in this case 50% earnings varied from before.
conclusion the above things are my own experience if you have any other thoughts please share here.
3. Adsense Placements: Placing many Ads above the fold increases CTR (percentages of views and click Generally CTR 4-5% means 4-5 clicks on 1000 views)but Decease CPC cost for click.
4.improper layout or theme: One of my website have over 20,000 visits a day earned 70% lower than other page have 7-8K visit per day. that’s the reason to we think about layout. proof added in another post linked below.
I have tied many experiments by weekly even withing a day also you can check my other post about how to improve adsense earnings.