The algorithm that is used to determine which friends you interact with – and so appear most often on your news feed.
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http://techcrunch.com/2010/04/22/facebook-edgerank/
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The social network’s news feed sorting filter is called EdgeRank. It helps Facebook keep users updated on friends’ activity without overwhelming them with every single post, “like,” and comment spilling out of their social graph.
It’s unclear when EdgeRank came into use, but a defining moment happened in 2010, when the company first provided public details on how it curates users’ news feeds.
The details are few, but what’s known is that the EdgeRank formula is based on how Facebook judges the closeness of two people (or a person and a brand), how valuable an activity is (sharing a photo is better than clicking “like,” for instance), and how long ago it took place. Precisely how these factors are measured is not revealed, and, like Google, Facebook is constantly making tweaks.
The algorithm is becoming important to marketers, who face pressure to justify the budgets being poured into Facebook. PageLever, a Facebook analytics company started in 2010, estimates that the average company page reaches fewer than 8 percent of its fans with updates. That could get worse, as more people post more content from smart phones, thereby cluttering feeds.
Zachary Welch, an expert at “news feed optimization theory and strategy” with the agency Brand Glue, says the highest figure he’s seen for a company’s posts reaching its Facebook fans is 39 percent, but most companies might top out in the low 20s.