Table 1.

Comparison of features between a complex system and a conventional system

	Conventional system	Complex system
Relationship of individual to system	System comprises discrete individuals, who are considered as distinct and statistically independent from each other, but who share the system environment	System comprises individuals, each interacting with others in the system; characteristics of the whole system emerge from these interactions
Context and culture	Context or culture seen as separate from the individuals and may be externally directed or imposed. Treated as a confounder or covariate in analysis	Context or culture seen as emergent properties of the system. In turn, these properties condition the interactions of individuals within the system
Predictability of response to events	Multiple independent responses to change produce a coherent average value response and an approximately normal distribution	Changes to the system are usually buffered by local interaction (so have minimal effect), but sometimes events spread through the system with unexpectedly large effects
Statistical Distributions	Normal distribution for continuous measures, Poisson distribution for events	Heavy-tailed distributions for events: typically inverse power law or log-normal