Tablet ads have twice the engagement of mobile ads

"The latest research from mobile video ad network Rhythm NewMedia provides  further evidence that tablet ads are more inviting than those on mobile phones. In its fourth-quarter report, the company said full-page display ads on tablets had a 21% engagement rate compared to 9.4% for the same ad units on smartphones.
Almost a quarter (24%) of tablet owners and 11% of smartphone owners have clicked an ad they were viewing on their respective devices to learn more about a product or promotion, according to data released last week by Nielsen. Doubling the screen size may not always double the interaction rate, but it seems to help.
Among other findings, the Rhythm report showed that combining video with full-page ads increased engagement on mobile devices from 9.4% to 11.5%. When it comes to in-stream video ads, it also indicated that adding custom buttons for social networks like Facebook or Twitter or specific brands pushed up engagement rates from .97% to 1.21%
Fifteen-second ads continued to have better completion rates than 30-second ads, but only slightly -- 89.2% compared to 88.3%. The shorter format still accounts for the vast majority of video ads, although 30-second spots grew slightly in 2011 in connection with people increasingly watching full episodes on mobile devices."

Source:  MediaPost, 1st March 2012