Re-examining the cascade problem: “... most of the time the system is completely stable, even in the face of external shocks. But once in a while, for reasons that are never obvious beforehand, one such shock gets blown out of all proportion in the form of a cascade.” contagion in a network is central to an outbreak of a cooperation or bursting bubble. need to examine the psychology of decision making People pay attention to one another when making up their minds, BUT it is the relative number (fraction) of people in a group choosing an alternative that is important.

Actual disease contagion events are independent of each other (vector -- increasing quickly and leveling off) but Decision infection follows a different probability law (a sigmoid). Thresholds can be due to: coercive externalities, market externalities, coordination externalities. Threshold values are distributed over the population (normal type distribution) You seek the opinion of others

Model – Diffusion of innovation. innovator node early innovator degree dependent threshold percolation cluster

“... in social contagion a system will only experience global cascades if it strikes a trade off between local stability and global connectivity.” Sensetivity of the upper boundary – too many neighbors reduces the ability to percolate (so many possible paths that they cannot connect) History as an information cascade – we should look at the surrounding network rather than the singular event. Trees send out very large number of seeds – few find the environment they can thrive in The seeds are not different the environment is. What is the network environment in 9/11, Enron,