Why CPA is an outdated measure of paid search

The paid search landscape has changed dramatically in recent years. The rise of mobile search, video consumption, social media channels and, ultimately, people-based marketing has meant there is a growing pressure for advertisers to be everywhere their audience is, and not just on that final Google search.
Last year, digital ad spend recorded growth of 14.3%, up to £14.5 billion. This is the eighth consecutive year of growth, and it's forecast to continue for the next two years at least. P