Designing Web Ads Using Click-Through Data
http://www.useit.com/alertbox/20010902.html

Nielsen, Jakob
Alertbox
2002

Abstract:

Search engine ads are one type of Web advertising that can actually work. To create the best ads, do quick experiments and redesign ads based on usability principles for online writing. Doing so helped us increase ad click-through by 55 to 310 percent.