Complex Contagions: A Decade in Review

TL;DR

This review summarizes a decade of research on complex contagions, highlighting empirical advances in social domains and theoretical developments in network topology, individual thresholds, and contagion interactions, while proposing future research directions.

Contribution

It provides a comprehensive synthesis of empirical and theoretical progress in complex contagion studies over ten years, and outlines key future research avenues.

Findings

Empirical studies have advanced understanding of contagion in health, social media, and politics.

Theoretical models now incorporate network topology and individual thresholds.

Future research should explore contagion interactions, threshold variability, and diversity effects.

Abstract

Since the publication of 'Complex Contagions and the Weakness of Long Ties' in 2007, complex contagions have been studied across an enormous variety of social domains. In reviewing this decade of research, we discuss recent advancements in applied studies of complex contagions, particularly in the domains of health, innovation diffusion, social media, and politics. We also discuss how these empirical studies have spurred complementary advancements in the theoretical modeling of contagions, which concern the effects of network topology on diffusion, as well as the effects of individual-level attributes and thresholds. In synthesizing these developments, we suggest three main directions for future research. The first concerns the study of how multiple contagions interact within the same network and across networks, in what may be called an ecology of contagions. The second concerns the study of how the structure of thresholds and their behavioral consequences can vary by individual and social context. The third area concerns the roles of diversity and homophily in the dynamics of complex contagion, including both diversity of demographic profiles among local peers, and the broader notion of structural diversity within a network. Throughout this discussion, we make an effort to highlight the theoretical and empirical opportunities that lie ahead.