How to Model Viral Growth: The Hybrid Model

I saw another name for viral growth factor K-factor

K-factor = i * c

i = number of invites sent by each customer (e.g. if each new customer invites five friends, i = 5)

c = percent conversion of each inbvite (e.g. if one in five invitees convert to new users, c = .2)

http://en.wikipedia.org/wiki/K-factor_(marketing)

Viral growth appears when K-factor > 1