frequency dependency

Frequency dependency is one of the most fundamental mechanisms of change in >networks and one of the characteristics of many approaches in evolutionary modelling (>simulation). Modelling approaches differ between local and global frequency dependency.

Local frequency dependency means that in a >population global patterns emerge out of the interaction between actors in different neighborhoods, with every actor only receiving impact and perceiving the patterns in that neighborhood or. A typical modelling device are cellular automata.

Global frequency dependency means that the behavior or a trait of actors is determined by the frequency of that behavior/trait in the entire population. The typical case is the logistic equation which results from models that assume a limited resource base for the spread of that trait such that the growth rate depends negatively on the share.

Frequency dependency is one cause of path dependency, as can be easily demonstrated with Polya urn models. In EE, frequency dependent modelling is very important in the analysis of the diffusion of technologies and of institutions. Frequency dependency can explain why economic change can "lock-in" into suboptimal states. Furthermore, frequency-dependency is directly related to the existence of multiple stable states of a system ("multiple equilibiria") and with the divergence of goals of action and emerging structures in the population.

Basic References
The classic on frequency-dependent phenomena in economics is:
Thomas C.Schelling, Micromotives and Macrobehavior, New York/London: Norton, 1978.

There are many websites where you can retrieve further information on modelling techniques and mathematical approaches to frequency-dependent phenomena - and where you can play with them! Some examples:
The logistic curve
Cellular automata
Schelling's segregation model

Semantic Field
network
frequency dependency   simulation