1. Advertising on the Web: Is there r esponse before click-through?;Briggs;Journal of Advertising Research,1997
2. Google 2005 http://adwords.google.com/support/bin/answer.py?answer=6111&topic=115
3. How to acquire customers on the Web;Hoffman;Harvard Business Review,2000
4. iProspect 2004 http://www.iprospect.com/premiumPDFs/iProspectSurveyComplete.pdf