The fake brand, called Quote Genie, was positioned as an online insurance broker providing a wide range of home, travel and motor insurance quotes.
Quote Genie was advertised in consumer guide Asrecommended Insurance, which was distributed to 600,000 prospects in January 2008.
Unique online visitors were recorded via the and calls were routed and recorded by a call lead manager. The ad did not appear in any other form apart from direct mail.
In total, more than 2,000 consumers responded to the ad. Of that number, 41% responded by visiting the website, rather than picking up the phone.
Ben Allan, managing director at Tilt, said: "This project is the first of its kind and finally shows a true measure of the affect offline media has on driving online response.
"We are seeing more and more consumers preferring to communicate online rather than via the phone, regardless of where they picked up a brand message.
"If brands don't apportion a percentage of online response back to offline media and instead just reduce offline investment, they will be making flawed marketing spend decisions."