Hey, Adsense isn't something I use much really, but I was thinking about this. It seems that adsense is paying less per click if a user is on facebook (Just for example) then goes on a website that has a highly paid CPC than if they were on a quality site just before visiting our sites. For example, lets say a medical site that pays a decent amount CPC, if the user is visiting a lot of other medical related sites previously, then on our site, the CPC would be higher than if they spent the day on Facebook and then went on the medical site once and clicked the same ad. Like I said, adsense isn't what I use, but it seems like it works that way. If so, what happens if the same user is browsing only medical sites but has facebook open in another tab (I normally have 20+ tabs open, 1 being facebook) - facebook reloads itself, so that would also be showing up with google and effecting the ads. Just an example, but something I thought about..
How are you able to determine that a click from a visitor who was just on Facebook is less than a visitor to your site who was on other medical sites? Seems to me this would be caused by Interest Based Ads. If you have IBA enabeld on Adsense, and someone comes to your site after being on a pet store website or a clothing site, there's a good chance they'll see some ads for pets/clothes when they get to your site. These clicks will most likely be significantly less than if they had been on a medical related site and were shown ads related to the medical niches. If you turn off interest based ads in you dashboard, you will only show ads on your site that are related to that site's content. Be careful with this however, because turning it off will shut it down for ALL OF YOUR ADS across all of your sites. This is something to consider.
Really depends on the site. Some sites you probably would only want ads being served that are directly related to the content. So having IBA off would take care of that. Other sites may perform just as well by showing ads related to a visitors previous web activity. Unfortunately you can't control this on a per site basis. You either have it on or off for all sites you're showing ads on.
Probably not. Since forums traditionally perform very poorly with Adsense, I'd want it turned on, so people would be shown ads related to other places they may have visited on the internet. With IBA turned off, a forum like Digital Point would only show hosting, domains, SEO etc. related ads. Forum users here are probably not going to click on those ads. Just my opinion. I could be totally wrong.