“From that fraction of ads that were matched, PwC found that, on average, nearly one in six (15%) of advertising pounds spent on these ads are being lost in the system. This “unknown delta” represents money that is spent on programmatic ads but can’t be found to have been delivered as an ad that an internet user has actually viewed.”
The full article is here.
One of the many reasons to have content and content experiences as a primary choice to grow your audience.