In 1998, two graduate students at Stanford University, Larry Page and Sergey Brin, developed "Backrub", a search engine that relied on a mathematical algorithm to rate the prominence of web pages. The number calculated by the algorithm, PageRank, is a function of the quantity and strength of inbound links.[22] PageRank estimates the likelihood that a given page will be reached by a web user who randomly surfs the web, and follows links from one page to another. In effect, this means that some links are stronger than others, as a higher PageRank page is more likely to be reached by the random web surfer.

Shifting the focus to the time span, we may need to measure some "Interim Metrics", which give us some insight during the journey itself, as well as we need to measure some "Final Metrics" at the end of the journey to inform use if the overall initiative was successful or not. As an example, most of social media metrics and indicators such as likes, shares and engagement comments may be classified as interim metrics while the final increase/decrease in sales volume is clearly from the final category.
Digital marketing is defined by the use of numerous digital tactics and channels to connect with customers where they spend much of their time: online. From the website itself to a business's online branding assets -- digital advertising, email marketing, online brochures, and beyond -- there's a spectrum of tactics that fall under the umbrella of "digital marketing."