Predicting lifespan of online communities

Through Shaping Tomorrow I found this study of what factors influence the longevity of online communities. "Researchers have previously claimed that there are too many variables influencing the survival or demise of such channels and that there is therefore no way of testing it, and earlier studies have primarily focused on group size and activity."

Turns out the key factor is how quickly the membership turns over -- the more frequently, at least to a point, the better. Those old friends, your first members, loyal as they are, don't contribute much to the life of the network, it seems.