39,889 research outputs found
Learning from the experience of others: an experiment on information contagion
Advances in stochastic system analysis have opened the way to a reconsideration of the processes through which behaviors spread in a population of individuals or organizations. One peculiar phenomenon affecting diffusion is information contagion (Arthur and Lane 1994). When agents have to choose on the basis of other people’s experience, rather than relying on their own direct observations, information externalities arise that drive towards the emergence of the arbitrary, stable dominance of one product over the competing one. We reproduced in controlled laboratory conditions the process of information contagion. The experiments show that when agents can only resort to the observation of other people’s experience in choosing between competing alternatives, the choice process generates some peculiar features: - information contagion among subjects generates self-reinforcing dynamics, amplifying initial asymmetries of products’ market shares; - this in turn produces path-dependent trajectories, highly dependent on early events in the choice sequence; - arbitrary asymmetric market shares tend to be stable in the long run, exhibiting lock-in phenomena; - agents choice criteria are heterogenous, giving rise to a mix of positive and negative feedback in the choice process, with the mix and the timing of such criteria affecting the final outcome
Statistical fluctuations in pedestrian evacuation times and the effect of social contagion
Mathematical models of pedestrian evacuation and the associated simulation
software have become essential tools for the assessment of the safety of public
facilities and buildings. While a variety of models are now available, their
calibration and test against empirical data are generally restricted to global,
averaged quantities, the statistics compiled from the time series of individual
escapes (" microscopic " statistics) measured in recent experiments are thus
overlooked. In the same spirit, much research has primarily focused on the
average global evacuation time, whereas the whole distribution of evacuation
times over some set of realizations should matter. In the present paper we
propose and discuss the validity of a simple relation between this distribution
and the " microscopic " statistics, which is theoretically valid in the absence
of correlations. To this purpose, we develop a minimal cellular automaton, with
novel features that afford a semi-quantitative reproduction of the experimental
" microscopic " statistics. We then introduce a process of social contagion of
impatient behavior in the model and show that the simple relation under test
may dramatically fail at high contagion strengths, the latter being responsible
for the emergence of strong correlations in the system. We conclude with
comments on the potential practical relevance for safety science of
calculations based on " microscopic " statistics
Competing contagion processes: Complex contagion triggered by simple contagion
Empirical evidence reveals that contagion processes often occur with
competition of simple and complex contagion, meaning that while some agents
follow simple contagion, others follow complex contagion. Simple contagion
refers to spreading processes induced by a single exposure to a contagious
entity while complex contagion demands multiple exposures for transmission.
Inspired by this observation, we propose a model of contagion dynamics with a
transmission probability that initiates a process of complex contagion. With
this probability nodes subject to simple contagion get adopted and trigger a
process of complex contagion. We obtain a phase diagram in the parameter space
of the transmission probability and the fraction of nodes subject to complex
contagion. Our contagion model exhibits a rich variety of phase transitions
such as continuous, discontinuous, and hybrid phase transitions, criticality,
tricriticality, and double transitions. In particular, we find a double phase
transition showing a continuous transition and a following discontinuous
transition in the density of adopted nodes with respect to the transmission
probability. We show that the double transition occurs with an intermediate
phase in which nodes following simple contagion become adopted but nodes with
complex contagion remain susceptible.Comment: 9 pages, 4 figure
Hipsters on Networks: How a Small Group of Individuals Can Lead to an Anti-Establishment Majority
The spread of opinions, memes, diseases, and "alternative facts" in a
population depends both on the details of the spreading process and on the
structure of the social and communication networks on which they spread. In
this paper, we explore how \textit{anti-establishment} nodes (e.g.,
\textit{hipsters}) influence the spreading dynamics of two competing products.
We consider a model in which spreading follows a deterministic rule for
updating node states (which describe which product has been adopted) in which
an adjustable fraction of the nodes in a network are hipsters,
who choose to adopt the product that they believe is the less popular of the
two. The remaining nodes are conformists, who choose which product to adopt by
considering which products their immediate neighbors have adopted. We simulate
our model on both synthetic and real networks, and we show that the hipsters
have a major effect on the final fraction of people who adopt each product:
even when only one of the two products exists at the beginning of the
simulations, a very small fraction of hipsters in a network can still cause the
other product to eventually become the more popular one. To account for this
behavior, we construct an approximation for the steady-state adoption fraction
on -regular trees in the limit of few hipsters. Additionally, our
simulations demonstrate that a time delay in the knowledge of the
product distribution in a population, as compared to immediate knowledge of
product adoption among nearest neighbors, can have a large effect on the final
distribution of product adoptions. Our simple model and analysis may help shed
light on the road to success for anti-establishment choices in elections, as
such success can arise rather generically in our model from a small number of
anti-establishment individuals and ordinary processes of social influence on
normal individuals.Comment: Extensively revised, with much new analysis and numerics The abstract
on arXiv is a shortened version of the full abstract because of space limit
Introduction to Judgment Aggregation
This introduces the symposium on judgment aggregation. The theory of judgment agÂgregation asks how several individuals' judgments on some logically connected propoÂsitions can be aggregated into consistent collective judgments. The aim of this introÂduction is to show how ideas from the familiar theory of preference aggregation can be extended to this more general case. We first translate a proof of Arrow's imposÂsibility theorem into the new setting, so as to motivate some of the central concepts and conditions leading to analogous impossibilities, as discussed in the symposium. We then consider each of four possible escape-routes explored in the symposium.Judgment aggregation, Arrow's theorem, Escape routes
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