In the two-plus years since the Media Rating Council announced it would develop standards to measure viewable impressions for digital advertising, there is more disagreement throughout the industry as to what constitutes a viewable ad than ever before.

Those MRC guidelines, which were issued in June, were merely a precursor to further debate around how digital advertising is measured. The MRC declared that half of a digital ad should be in view for at least one second to be considered viewable. Meanwhile, Unilever and its marketing agency GroupM in November raised the stakes and said they would only buy ads that were 100 percent viewable in a browser.

Just this week the Interactive Advertising Bureau issued a report stating that 100 percent viewability “isn’t possible” and instead is offering 70 percent as a goal for 2015.

As per AdExhanger:

“The IAB is calling 2015 a “year of transition,” a time when the advertising community – advertisers, publishers, agencies and tech vendors alike – should work together to make viewability into a currency that serves the needs of all stakeholders.”

The heart of the debate remains the murkiness of what actually defines viewability. The definition of a viewable impression, of course, depends on the type of the ad units as well the reporting system. Different vendors have systems that use differing criteria in reporting an ad as being viewed.

Ultimately, no one can blame advertisers for wanting actual humans to see their ads and receiving a full return on investment. At the same time, publishers are wary of having to over-deliver to agencies that hold a stringent view of what constitutes a viewable impressions without being compensated as they try to make good. This is a conversation that will likely continue to evolve throughout 2015, and the industry will be keeping a close eye.