Complex Contagions and the Diffusion of Innovations

Evidence from a Small-N Study

20th March 2019
Versione stampabile

Venue: Department of Sociology and Social Research, via Verdi, 26 - Trento,  Meeting Room – III floor
Time: 12:00 - 14:00

Brown bag seminars - Organized by the Center for Social Inequality Studies (CSIS) research unit


  • Gianluca Manzo - CNRS & University of Paris-Sorbonn

The recent literature on “complex contagions” challenges Granovetter’s classic hypothesis on the strength of weak ties and argues that, when the actors’ choice requires reinforcement from several sources, it is the structure of strong ties that really matters to sustain rapid and wide diffusion. The paper contributes to this debate by reporting on a small-N study that relies on a unique combination of ethnographic data, social network analysis, and computational models. In particular, we investigate two rural populations of Indian and Kenyan potters who have to decide whether to adopt new, objectively more efficient and economically more attractive, technical/stylistic options. Qualitative field data show that religious sub-communities within the Indian and Kenyan populations exhibit markedly different diffusion rates and speed over the last thirty years. To account for these differences, we first analyze empirically observed kinship networks and advice networks, and, then, we recreate the actual aggregate diffusion curves through a series of empirically calibrated agent-based simulations. Combining the two methods, we show that, while single exposure through heterophyllous weak ties was sufficient to initiate the diffusion process, large bridges made of strong ties can in fact lead to faster or slower diffusion depending on the type of signals circulating in the network. We conclude that, even in presence of “complex contagions,” dense local ties cannot be regarded as a sufficient condition for faster diffusion.

Gianluca Manzo is a permanent research fellow in sociology at the CNRS (Centre National de la Recherche Scientifique) as a member of the GEMASS (Groupe d’Etude des Méthodes de l’Analyse Sociologique de la Sorbonne), where he leads the research axis on Social Mechanisms and Actors’ Rationality. Since August 2018, he is the GEMASS’s deputy director. He earned a PhD in Epistemology and Methodology of Social Sciences (2006) from the University of Trento, as well as an M.Phil in Social Sciences and Philosophy of Knowledge (2002) and a PhD in Social Sciences (2006) from the University of Paris-Sorbonne. He held visiting positions and/or taught at the University of Oxford (Nuffield College), University of Oslo, Universitat Autònoma de Barcelona, University of Roma-La Sapienza, Columbia University, University of Mannheim, Instituto de Filosofía y Ciencias de la Complejidad (Santiago of Chile), University of Cologne, and European University Institute. His research concern theoretical and empirical topics at the intersection of several fields, namely: philosophy of social sciences (models and mechanisms), sociological theory (analytical sociology and theory of action), and social stratification (educational inequalities, inequality perception, status hierarchies). His current projects deal with migration dynamics and the diffusion of innovations. He is an expert of agent-based computational simulation.