Cognitio has several web sites, where the (by far) biggest are: WordMine.info, FindTheWord.info, and Kryssakuten.se (in Swedish). These pages started many (in internet time) years ago, mostly as a hobby and a proof-of-concept and have since then grown in both content and visitors.
These pages are being economically supported by ads and without the ads the pages would not exist. There are probably several hundred of ad networks out there, and most of them wants to show their ads on your page. Knowing which one to use can be time-consuming and also make you loose money displaying ads from badly performing ad networks.
So when we find a network that we think might be interesting we will test them before deciding if we shall continue to show their ads. After doing these tests for several years, we have decided to do these tests in a more well documented manner. And also display the result here, so others that are considering these ad networks get a hint of how there perform before they spend time testing them.
The ad networks that we are looking for is the ones with automated ad displays. These web sites are not our main area and we do not have time to check each ad and product to select the ones that we think will be best for the site. So these tests will only show the result of the automatic ad serving. If we had time to look for specific ads that would perform on the site, the result would probably be completely different.