Additionally, the interactivity inherent in digitally delivered ads can allow advertisers to view, in real time, whether ads are being viewed, clicked and accessed, as well as allowing them to change ads depending on the success or otherwise of an ongoing campaign.
The lower cost of Google's mobile ads compared with those viewed on a desktop have contributed to an overall downturn in the average amount paid by advertisers every time someone clicks on an ad, the company has said.
But the leftover ads might as well have been pitching the thousands of cancer doctors who viewed them while en route to this month's American Society of Clinical Oncology meeting, held in the same convention center.