Depending of the network we decide which of our sites the new ad network will be tested on. Then the top banner (it is often the best performing ad space) on the site will alternate the new ads with Google Adsense ads so they are displayed roughly the same number of times. If the tested ad network is not performing absolutely rock bottom, or displaying ad with offensive contents, it will normally be tested for about a week.
The number of times the ads are displayed are tracked with events in Google Analytics. It will count the number of time the ad network script was run on the site, regardless if it actually displayed an ad or not. But an ad network not displaying ads every time is also a waste of ad space.
We cannot keep track of the number of clicks in Google Analytics, so we have to rely on the ad network for that.
The revenue of the ad network is what it all comes down to. No amounts will be displayed. Instead we will show how well the new ad network performed compared to Google AdSense in percent. If the tested network displays it revenue in a different currency than Google AdSense, the amount will first be converted at google.com.
These tests actually only measures how well the different ad network perform on the tested site during the measured period. It does not show how its performance is on other sites or other periods, but it gives a hint of how the ad network performs compared to Google AdSense.