The lads 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. Completion rates for in-stream ads on the two major smartphone platforms — Android and iOS — were also fairly close, with the former at 92% and the Apple operating system at 87%. Rhythm said more than three-quarters (76%) of campaigns on its network include in-stream video ads, which appear as a commercial break for full episodes or as pre-rolls. The company also noted that ad requests for the network in the fourth quarter tripled from a year ago and that the sell-through rate was strong on premium properties. Rhythm works with publishers including ABC, IAC, Demand Media and Warner Bros. On the advertising side, it has clients such as Chase, McDonald’s, General Motors and AT&T.