As online advertising has grown from an experiment on a marketer’s checklist to a critical tool in the proverbial toolbox, so has the demand for actionable metrics of performance.
At first, measuring engagement was straightforward. A site serves a user an ad (delivered by an unbiased third-party, the ad server), and a user clicks on that ad to go to whatever page the marketer desired. Ad servers then collect the number of clicks and impressions, which serves two primary purposes. The first is that marketers use these numbers to draw insights into how their campaigns are performing. The second is that marketers pay their advertising partners based on things like number of clicks.
Soon, marketers clamored to gain deeper insights. Technology vendors introduced cookies to attribute actions on the site, such as a product purchase or online signup, called a “conversion,” to an ad impression or click. It’s this process — attributing actions on a site to ad impressions and clicks — where things get tricky, and which this blog post will attempt to explain.