As shoemoney has brought up many times, Adsense is typically not the most efficient option to generate revenue on your website (simply follow the money and you’ll know why).  However, it is nice for people who aren’t used to internet advertising because Google allows you to setup advertising in minutes and you can generate revenue right away.  On a couple of my smaller sites, I still use Adsense, simply because I haven’t found anything that compares to it for the size of my site.  For example, last month with Adsense, I averaged well over $50 CPM on one of my sites.  I’ve tried affiliate marketing on it, and am yet to have any luck.  But with the return that Adsense is giving, I can’t complain.

Recently, I’ve been integrating Ad Manager into all of my sites, simply because Ad Manager is amazing.  If you run a website and aren’t using Ad Manager, you’re missing out.  Anyways, with Ad Manager, any ad slots that aren’t purchased by an advertiser can be filled with Adsense.  Even slots that have competing advertisers rotating can have Adsense rotated in so that Ad Manager can find out which type of ad will give you the best CPM value (between competing all of the advertisers, as well as Adsense).

So the other day I integrated Ad Manager into one particular site and set it up so that the slots just filled with Adsense (since I have no direct advertisers for this site).  I assumed the earning results would be no different than just using the standard script from Google Adsense itself.  After a couple days of testing, I realized that for some reason, the Ad Manager script that was filling slots with Adsense was performing at nearly half the value that the standard Adsense was.  I’m not sure why this is (the CTR on the ads was cut in half, which leads me to believe that the ads that were being displayed weren’t targetted as well).

Does anyone know why the Ad Manager would return different ads than the standard Adsense code?