Abstract
Tie strengths in social networks are heterogeneous, with strong and weak ties
playing different roles at both the network and the individual level.
Egocentric networks, networks of relationships around a focal individual,
exhibit a small number of strong ties and a larger number of weaker ties, a
pattern that is evident in electronic communication records, such as mobile
phone calls. Mobile phone data has also revealed persistent individual
differences within this pattern. However, the generality and the driving
mechanisms of this tie strength heterogeneity remain unclear. Here, we study
tie strengths in egocentric networks across multiple datasets containing
records of interactions between millions of people over time periods ranging
from months to years. Our findings reveal a remarkable universality in the
distribution of tie strengths and their individual-level variation across
different modes of communication, even in channels that may not reflect offline
social relationships. With the help of an analytically tractable model of
egocentric network evolution, we show that the observed universality can be
attributed to the competition between cumulative advantage and random choice,
two general mechanisms of tie reinforcement whose balance determines the amount
of heterogeneity in tie strengths. Our results provide new insights into the
driving mechanisms of tie strength heterogeneity in social networks and have
implications for the understanding of social network structure and individual
behavior.
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