The competition for attention
Paradoxically, measurement is becoming an ever more complex business in the digital environment, which once promised to be able to quantify matters in a verifiable way that traditional media struggled with. But as the arguments over viewability demonstrate, that has not proved to be the case. Sir Martin Sorrell, for example, has been scathing of the standards applied to digital media – is 50% of a banner ad in view for a second (and even then maybe not noticed) really an adequate measure of anything? – compared to those pertaining to other media.
So simply having an opportunity to see may not in the end tell advertisers very much. The next logical step is to calculate the time spent with an ad. But this too is fraught with difficulties: in a multi-device world it's perfectly possible to spend time with an ad yet be totally unaware of its existence.