In an advisory note following a pilot test of viewable impression measurement, MRC cautioned that this inconsistency needs to be overcome “before finalising a new online advertising currency definition”.

MRC said that the number of impressions in a campaign for which viewability cannot currently be determined is “often significant”. It’s pilot test involved 22 ad campaigns, accounting for more than 3bn served impressions between them. Five unnamed viewability measurement vendors participated.

It found that viewable rates for live campaigns showed “tremendous variability”, ranging from 78.6% to 7.8%, while the ability to measure whether impressions were viewable or not ranged from 0% to 77%.

Based on this work, the MRC said it would be premature of the advertising industry to begin using viewability measures for buying and selling.

“Moving to a new, as yet not fully measurable currency on a wholesale basis at this juncture could do more harm than good,” the MRC said.

Advertisers, agencies and media owners are starting down this road, however. In October, Gannett – the publisher of USAToday.com – struck a deal with ComScore to deliver viewable impression measurements for online ad campaigns, while Publicis’ digital marketing R&D arm Vivaki Nerve Center agreed a similar deal on behalf of its clients.