Nowadays, we have a vast variety of options regarding the programs we use for online advertising. These will likely become more available and change as the industry develops. However, this sometimes makes it hard for industry professionals to choose which program will be a better fit for the goals of the kind of project they are working on. 

For this reason, some of the most valuable web posts out there are those where other industry professionals conduct tests and review them on our behalf. Makes it easier for us, doesn’t it?

Well, one of our colleagues did a manual A/B test of putting AdSense and Google AdX (Ad Exchange) on his site and comparing the two. Google vs. Google! In his review, he considered several aspects that differentiated the two. 

What makes this test noteworthy is the insights into the difference between money made and general action towards the ad. It is important to consider that AdSense made more money on an RPM/per-impression basis. What’s more, is that AdX gave around sixty-five percent more clicks, yet paid around thirty-five percent less per click. This is a notable difference since you would assume that auctions would lead to comparable CPCs. 

To the newbie, this might seem surprising at first glance. Considering that AdSense is mainly used for smaller sites, while AdX is utilized for bigger ones. Considering this idea, AdX should have access to much greater inventory and, thus, the ability to bid up each impression for more. 

Various people working in the industry can respond confirming that this is their experience. Even I conducted similar tests that turned up similar results. But that was more than two years ago, so the possibility that things may have changed along the way existed. Apparently, they didn’t change so much. 

From my perspective, the main hypothesis to explain this is to look at the converse side of a piece of conventional ad publishing wisdom. AdX and the ad exchanges tend to be more optimized to get a large number of people to view their ads, not perform a specific action such as clicking on the ads. For this reason, the converse of the same observation is that publishers may get more impressions than are available if they use AdX but, make less per impression. 

Other likely possibilities: AdSense has better fraud control compared to AdX. Or perhaps Google is playing more sketchy games on the larger AdX level than the smaller AdSense level? Giving its network a subtle advantage in the bidding?

Given that Google will always be a Black Box to us, we may never know the specific reasons behind this. But the idea reinforces the wisdom that we should ABT: Always Be Testing. Even when we suspect that X may work better than Y, there may be confounding factors that we don’t even know about. Factors that lead to a different result in this particular case.