Screen size is a major factor determining whether people watch preroll ads.

Prerolls, placed in front of online video content that people want to watch, present a dilemma to media owners and advertisers alike.

Non-skippable prerolls, although popular among content owners, risk driving people away altogether, missing out on both the ad and the video that follows.

Skippable ads, favored by YouTube which makes about 70% of its ad revenue that way, are consumer-friendly options, but make reach and frequency targets for ad campaigns much harder to reach.

About 80% of YouTube ads end up being cut short by viewers.

Screen Size Matters

Another key factor is influencing people’s behavior, however – screen size.

People are likely to react to preroll in different ways, depending on which screen they’re looking at, reports TubeMogul, a video ad tech specialist that analyzed traffic moving through its system from October to December last year.

During a non-skippable preroll, people watching on a desktop are much more likely to stick around than viewers watching on mobile devices, TubeMogul analysts found.

The tables are turned however, once the preroll becomes skippable.

Here, desktop viewers are the most likely to go straight to the content. Tablet viewers, by comparison, are 2.5 times likely than desktop viewers to let the ad play.

"Targeting and inventory availability will also affect marketers' tactics," Laura Crane, TubeMogul's senior research associate, wrote in a blog post, Screen Size Matters.

"The key is to know what to expect when you reach the person on the other side of the device."

More on when people avoid prerolls or let them play in the slideshow below.