A new document has been added to the Society for Political Methodology  
Website.

Title:     The “Unfriending” Problem: The Consequences of Homophily in  
Friendship Retention for Causal Estimates of Social Influence

Author(s):     Hans Noel, Brendan Nyhan

Entry Date:     2010-07-08

Keyword(s):     contagion, homophily, monte carlo, peer effects,  
simulation, social networks


Abstract:      Christakis, Fowler, and their colleagues have recently  
published numerous articles estimating “contagion” effects in social  
networks. In response to concerns that their results are driven by  
homophily, Christakis and Fowler describe Monte Carlo results showing  
no evidence of homophily-induced bias in their statistical model’s  
estimates of peer effects. However, their simulations do not address  
the role of homophily in friendship retention, which may cause  
significant problems in longitudinal social network data. We  
investigate the effects of this mechanism using Monte Carlo  
simulations and demonstrate that homophily in friendship retention  
induces significant upward bias and decreased coverage levels in the  
Christakis and Fowler model if there is non-negligible attrition over  
time.	

http://polmeth.wustl.edu/mediaDetail.php?docId=1183

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