I don’t have much to say on this, except Alexis Madrigal did a great job putting what I’ve been thinking (for a while) into words: Dark Social: We Have the Whole History of the Web Wrong.

We often become so obsessed with metrics that we forget that, akin to advertising in the “real world,” we cannot measure everything.

I would wager that your spread in the dark social correlates to your spread in Facebook/Twitter.