Strong ties in a small world

This paper examines the celebrated ‘Strength of weak ties’ theory of Granovetter (1973). We examine two hypotheses implied by the theory: one, for any three players with two links present, the probability of a third link being present is increasing in the strength of the two ties, and two, the removal of a weak tie breaks more shortest paths than the removal of a strong tie. This paper tests these hypotheses using data on coauthorship among economists. Our data supports the hypothesis of transitivity of strong ties, but it rejects the hypothesis that weak ties are more crucial than strong ties. We then propose an explanation for the strength of strong ties which builds on two properties of the network: one, significant inequality in the distribution of connections across individuals and, two, stronger ties among highly connected individuals. ∗Dpto. Fundamentos del Análisis Económico, Universidad de Alicante. E-mail: [email protected]. †Faculty of Economics, University of Cambridge, and Christ’s College. E-mail: [email protected]. We thank the editor, Tom Snijders, and two anonymous referees for very helpful suggestions. We are also grateful to Francis Bloch, Vincent Buskens, Antoni Calvó-Armengol, Dennis Fok, Matthew Jackson, Willemien Kets, Marcel Fafchamps, Alan Kirman, Michael Kosfeld, Richard Paap, Werner Raub and seminar participants at Erasmus University, Mannheim, Marseille, Oxford, Utrecht, and ICTP (Trieste) for helpful discussions and comments. Marco van der Leij would like to thank the Spanish Ministry of Science and Innovation (grant SEJ2007-62656) for financial support.