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FYI, Barry
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---------- Forwarded message ----------
Date: Wed, 03 Sep 2003 15:26:51 +0200
From: Karl M. van Meter <[log in to unmask]>
To: [log in to unmask]
Subject: Article - On Global Social Networks, Dodds et al (Science)
Thanks to Science Week 5 September 2003
SOCIOLOGY: ON GLOBAL SOCIAL NETWORKS
The following points are made by P. Sheridan Dodds et al (Science
2003 301:827):
1) It has become commonplace to assert that any individual in the
world can reach any other individual through a short chain of
social ties. Early experimental work by Travers and Milgram
(1969) suggested that the average length of such chains is
roughly six, and recent theoretical and empirical work has
generalized the claim to a wide range of nonsocial networks.
However, much about this "small world" hypothesis is poorly
understood and empirically unsubstantiated.
2) In particular, individuals in real social networks have only
limited, local information about the global social network and,
therefore, finding short paths represents a non-trivial search
effort.
3) Moreover, and contrary to accepted wisdom, experimental
evidence for short global chain lengths is extremely limited. For
example, Travers and Milgram reported 96 message chains (of which
18 were completed) initiated by randomly selected individuals
from a city other than the target's. Almost all other empirical
studies of large-scale networks, have focused either on nonsocial
networks or on crude proxies of social interaction such as
scientific collaboration, and studies specific to e-mail networks
have so far been limited to within single institutions.
4) In summary: The authors report on a global social-search
experiment in which more than 60,000 e-mail users attempted to
reach one of 18 target persons in 13 countries by forwarding
messages to acquaintances. The authors find that successful
social search is conducted primarily through intermediate to weak
strength ties, does not require highly connected "hubs" to
succeed, and, in contrast to unsuccessful social search,
disproportionately relies on professional relationships. By
accounting for the attrition of message chains, the authors
estimate that social searches can reach their targets in a median
of five to seven steps, depending on the separation of source and
target, although small variations in chain lengths and
participation rates generate large differences in target
reachability. The authors conclude that although global social
networks are, in principle, searchable, actual success depends
sensitively on individual incentives.
--------------------------------
COLLECTIVE DYNAMICS OF "SMALL-WORLD" NETWORKS.
The following points are made by D.J. Watts and S.H. Strogatz
(Nature 1998 393:440):
1) Networks of coupled dynamical systems have been used to model
biological oscillators, Josephson junction arrays,, excitable
media, neural networks, spatial games, genetic control networks
and many other self-organizing systems. Ordinarily, the
connection topology is assumed to be either completely regular or
completely random. But many biological, technological and social
networks lie somewhere between these two extremes.
2) The authors explore simple models of networks that can be
tuned through this middle ground: regular networks "rewired" to
introduce increasing amounts of disorder. The authors find that
these systems can be highly clustered, like regular lattices, yet
have small characteristic path lengths, like random graphs. The
authors call them "small-world" networks, by analogy with the
small-world phenomenon, (popularly known as six degrees of
separation). The neural network of the worm Caenorhabditis
elegans, the power grid of the western United States, and the
collaboration graph of film actors are shown to be small-world
networks.
3) Models of dynamical systems with small-world coupling display
enhanced signal-propagation speed, computational power, and
synchronizability. In particular, infectious diseases spread more
easily in small-world networks than in regular lattices.
--------------------------------
CLASSES OF SMALL-WORLD NETWORKS.
The following points are made by L.A. Amaral et al: (Proc. Nat.
Acad. Sci. 2000 97:11149):
1) The authors report a study of the statistical properties of a
variety of diverse real-world networks. The authors present
evidence of the occurrence of three classes of small-world
networks: (a) scale-free networks, characterized by a vertex
connectivity distribution that decays as a power law; (b) broad-
scale networks, characterized by a connectivity distribution that
has a power law regime followed by a sharp cutoff; and (c)
single-scale networks, characterized by a connectivity
distribution with a fast decaying tail.
2) The authors note for the classes of broad-scale and single-
scale networks that there are constraints limiting the addition
of new links. The authors suggest their results indicate that the
nature of such constraints may be the controlling factor for the
emergence of different classes of networks.
ScienceWeek http://www.scienceweek.com
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* Karl M. van Meter BMS, Bulletin de Methodologie Sociologique
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* LASMAS-CNRS RC33, Research Committee Logic &
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