BALTIMORE, MD: The debate on the viewability of digital ads has taken another turn with the announcement by Millennial Media, the mobile ad marketplace, that it is to offer a 100% viewability guarantee for in-app mobile advertising campaigns.

It will work with Integral Ad Science as its measurement partner; IAS recently completed an audit of the Millennial network and both companies have been working with publishers on technical changes that improve viewability.

"Mobile has quickly become the first screen and most accessed device," said Scott Knoll, President & CEO at Integral Ad Science. "As such, viewability in mobile is more important than ever."

Michael Barrett, President & CEO at Millennial Media added that "the mobile ad ecosystem is desperately seeking guidelines around viewability" and claimed "we are choosing the highest standard possible by offering a 100% in-app viewability guarantee".

Advertisers have been pushing for higher viewability standards than the current guidelines, which state that half of a display ad must be in view for at least one second, while half a video ad must be in view for at least two seconds.

In November last year FMCG giant Unilever raised the bar, requiring 100% of a display ad to be in view; ditto for video but additionally, a person must click to start it rather than having it play automatically, and then they must play at least half the ad with the sound on.

Google too anticipates the industry will move to 100% viewability, possibly during 2015, but Jane Hong, Google DoubleClick's head of industry for CPG advertisers, has cautioned against raising unrealistic expectations.

"There are some limitations today as far as potential scale loss if you do it [just switch to 100% viewability]," she said. "The question is, at what price of inventory does that [100% viewability] make sense? How much inventory is there really at that point?"

Whatever the particular reservations the trend is irreversible. "The responsibility of viewability falls on us all," said Shenan Reed, President Digital, North America at media agency network MEC.

"Brands, agencies, publishers, ad tech vendors, and industry organizations all need to work together to push this forward and create industry-wide adoption."

And as that happens, so advertisers will develop more confidence. "As we build trust in mobile, the ad dollars will finally catch up to consumer behaviour," stated Jason Kelly, President of Managed Media at Millennial Media.

Data sourced from Millennial Media; additional content by Warc staff