How to easily quantify the precise value of display advertising

Proving the value of 'display' without running a time and budget consuming test has always been difficult. But no more. The below analysis can not only prove display's worth but it can precisely quantify it too, and all it needs is DCM, GA360 and about a day.
One of the most common questions we get as an agency is how can you prove that seeing an ad does actually affect customers and increase the likelihood of them converting.
The best way to answer this is with a placebo test: you spl