A lot of folks have asked for more details on the way we measured and optimized viral app growth in the Stanford class I co-taught recently. So here's a bit more info on methodology for measuring virality and what it means for an app to "go viral."
K-factor and R-zero
Terms like "K-factor" (contagion) and "R-zero" (reproduction rate) are often used to describe the growth rate of viral apps. These terms come from the fields of medicine and biology -- they're originally intended to describe the spread of of viral diseases, but they're nice analogies for how web/SN apps grow. Some would even describe widgets and apps as "diseases" that have "corrupted" popular social networks like MySpace and Facebook! ;-) Of course, having worked at Slide and authored some FB apps of my own, that's clearly not my belief... So, read on if you're interested in viral apps!
[digg=http://digg.com/programming/The_Four_Viral_App_Objectives]
