From Will Oremus’s insightful story How Facebook’s news feed algorithm works:

Facebook’s data scientists were aware that a small proportion of users—5 percent—were doing 85 percent of the hiding. When Facebook dug deeper, it found that a small subset of those 5 percent were hiding almost every story they saw—even ones they had liked and commented on. For these “superhiders,” it turned out, hiding a story didn’t mean they disliked it; it was simply their way of marking the post “read,” like archiving a message in Gmail.

This reminds me of a story I read a while back about how tons of people flagged and reported news stories about Lance Armstrong for “drug abuse”. This is why qualitative research is so incredibly important. Analytics can never tell us the whole story.