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Dear All,

Several on this list may be interesting in this paper we just published 
in PNAS. It develops a method for distinguishing peer influence from 
homophily in large dynamic networks. We apply it to 27 million users of 
Yahoo's instant messaging graph to predict influence in the adoption of 
a new mobile service application. Enjoy:)

"Distinguishing Influence Based Contagion from Homophily Driven 
Diffusion in Dynamic Networks"


Node characteristics and behaviors are often correlated with the
structure of social networks over time. While evidence of this type of
assortative mixing and temporal clustering of behaviors among linked
nodes is used to support claims of peer influence and social contagion
in networks, homophily may also explain such evidence. Here we develop
a dynamic matched sample estimation framework to distinguish influence
and homophily effects in dynamic networks, and we apply this
framework to a global instant messaging network of 27.4 million
users, using data on the day-by-day adoption of a mobile service
application and users’ longitudinal behavioral, demographic, and
geographic data. We find that previous methods overestimate peer
influence in product adoption decisions in this network by 300–700%,
and that homophily explains 50% of the perceived behavioral contagion.
These findings and methods are essential to both our understanding of
the mechanisms that drive contagions in networks and our knowledge of
how to propagate or combat them in domains as diverse as epidemiology,
marketing, development economics, and public health.

Sinan Aral
Assistant Professor, NYU Stern School of Business.
Research Affiliate, MIT Sloan School of Management.
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