The micro-mechanisms underpinning growth and decline in a social network: does leaving mirror joining?

Griffith Rees, Felix Reed-Tsochas


Over time, the majority of social systems go through periods of growth and decline. Whereas there are plenty of studies on the micro-level mechanisms underpinning growth, periods of macro-level decline and the micro-level mechanisms that may generate them are considerably understudied. And by extension: the micro-mechanisms that encourage individuals to join the system during macro-level growth may compete with micro-level mechanisms that encourage leaving the system, and those same leaving mechanisms may just have greater strength than joining mechanisms when the system declines. In short: does the process of a system growing at the macro-level reflect the process by which that system declines? We explore this question with a large longitudinal dataset covering the growth and decline of a social system called FidoNet, where messages were sent over phone lines prior to the birth of the World Wide Web using a technology called Bulletin Board Systems (BBSs). With week-level records from the creation of the system through its peak and significant decline, we model the growth phase and decline phase of the system. In parallel with other findings on social system growth, social and spatial contagion appears to play a significant role in how System Operators (sysops, people who managed BBSs) joined FidoNet. We compare that to the decline phase suggesting some symmetry in the contagious process that encouraged areas to leave the system, but with some resilience, even as the World Wide Web came to dominant digital social interaction.

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