Watts threshold model

Watts threshold model is a formal model of social contagion introduced by Duncan Watts in 2002, extending Mark Granovetter's 1978 threshold framework to networked populations. In the model, each individual has a personal threshold for adopting a behavior — the fraction of their neighbors who must already have adopted before they follow. The global outcome depends on the interaction between the distribution of individual thresholds and the topology of the social network. The model demonstrates that even small initial perturbations can trigger global cascades when the network's threshold distribution and degree structure create a critical mass of early adopters capable of chain-reaction propagation. The Watts threshold model bridges sociology and physics by treating revolutions, fads, and market bubbles as the same dynamical species. What the model obscures — and what adaptive threshold extensions later revealed — is that treating thresholds as fixed parameters ignores the learning and memory that reshape vulnerability in real populations. A threshold is not a property of a person; it is a property of a person in a history.