What about private messages? I mean we know Facebook tracks those too. Do they just not want to admit as much publicly?
"Relationships start with a period of courtship: on Facebook, messages are exchanged, profiles are visited, posts are shared on each other's timelines."
They didn't produce any graphs of the amount of messages exchanged though.
[1] https://www.facebook.com/notes/facebook-data-science/the-for...