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Published August 9, 2017 | Submitted
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Search in the Formation of Large Networks: How Random are Socially Generated Networks?

Abstract

We present a model of network formation where entering nodes find other nodes to link to both completely at random and through search of the neighborhoods of these randomly met nodes. We show that this model exhibits the full spectrum of features that have been found to characterize large socially generated networks. Moreover, we derive the distribution of degree (number of links) across nodes, and show that while the upper tail of the distribution is approximately "scale-free," the lower tail may exhibit substantial curvature, just as in observed networks. We then fit the model to data from six networks. Besides offering a close fit of these diverse networks, the model allows us to impute the relative importance of search versus random attachment in link formation. We find that the fitted ratio of random meetings to search-based meetings varies dramatically across these applications. Finally, we show that as this random/search ratio varies, the resulting degree distributions can be completely ordered in the sense of second order stochastic dominance. This allows us to infer how the relative randomness in the formation process affects average utility in the network.

Additional Information

We gratefully acknowledge financial support under NSF grant SES-0316493, the Lee Center for Advanced Networking, and a SISL/IST fellowship. We thank David Alderson, Hawoong Jeong, Sanjeev Goyal, Marco van der Leij, and Jose Luis Moraga-Gonzalez for making data available. We thank Steven Durlauf for a helpful discussion of the paper and Antoni Calvo-Armengol, Matthias Dahm, Dunia Lopez-Pintado, Fernando Vega-Redondo, and Duncan Watts for helpful comments and conversations.

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August 19, 2023
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January 13, 2024