There's a post at the Outbrain blog, What do readers really want?, which reasons why contextual relations among documents is not necessarily the most interesting content for readers when being recommended for additional content. Apparently, the related contextual related content is less appealying to readers than the behavioral related content.
* Popularity: recommending content that is trending up in popularity on the site
* Contextual: recommending content related to the page the person is currently on
* Behavioral: recommending content based on audience dynamics. For instance, finding content that people with similar reading habits have been consuming, that is not mainstream popular, and that the person has not read before
* Personal: recommending content within broad categories that the person frequents but not necessarily related to the page they are on at present
When evaluating success, we look at a couple of metrics.
1. How frequently do people click on links based on the algorithmic approach (CTR, or “click through rate”)
2. How many more pieces of content does the person consume on the site *after* clicking on the link (what we call PVAC, or “pageviews after the click”)
Check out that post: What do readers really want? by David Sasson.