Michael W. Macy

Computational Social Science

A field is emerging that leverages the capacity to collect and analyze data at a scale that may reveal patterns of individual and group behaviors.

Complex Contagions and the Weakness of Long Ties

The strength of weak ties is that they tend to be long—they connect socially distant locations, allowing information to diffuse rapidly. The authors test whether this “strength of weak ties” generalizes from simple to complex contagions. Complex contagions require social affirmation from multiple sources. Examples include the spread of high‐risk social movements, avant garde fashions, and unproven technologies. Results show that as adoption thresholds increase, long ties can impede diffusion. Complex contagions depend primarily on the width of the bridges across a network, not just their length. Wide bridges are a characteristic feature of many spatial networks, which may account in part for the widely observed tendency for social movements to diffuse spatially.

Diurnal and Seasonal Mood Vary with Work, Sleep, and Daylength Across Diverse Cultures

Across the world the collective mood heightens at breakfast time and during the weekend. We identified individual-level diurnal and seasonal mood rhythms in cultures across the globe, using data from millions of public Twitter messages. We found that individuals awaken in a good mood that deteriorates as the day progresses—which is consistent with the effects of sleep and circadian rhythm—and that seasonal change in baseline positive affect varies with change in daylength. People are happier on weekends, but the morning peak in positive affect is delayed by 2 hours, which suggests that people awaken later on weekends.

Life in the network: the coming age of computational social science

A field is emerging that leverages the capacity to collect and analyze data at a scale that may reveal patterns of individual and group behaviors.

In Search of Excellence: Fads, Success Stories, and Adaptive Emulation1

The faddishness of the business community is often noted and lamented but not well understood by standard models of innovation and diffusion. We combine arguments about organizational cognition and institutional mimicry to develop a model of adaptive emulation, where firms respond to perceived failure by imitating their most successful peers. Computational experiments show that this process generates empirically plausible cascades of adoption, even if innovations are entirely worthless. Faddish cycles are most robust across alternative treatments of managerial decision making where innovations have modest positive effects on outcomes. These results have broad implications for the faddishness of a business community increasingly marked by media‐driven accounts of success, and for the properties of organizational practices that are hot one day and cold the next.

Network Diversity and Economic Development

Network for Recovery A long-standing theory suggests that social diversity leads to economic development. By combining the United Kingdoms telephone communication records (both landline and mobile) with information on regional economic conditions, Eagle et al. (p. 1029) demonstrate that network diversity alone accounts for over three-quarters of the variance of a regions economic status. Although the data cannot be used to show causality, the association suggests that economic development and recovery may depend not solely on monetary stimulus but also on the development of a nations social infrastructure. Social diversity is associated with economic development. Social networks form the backbone of social and economic life. Until recently, however, data have not been available to study the social impact of a national network structure. To that end, we combined the most complete record of a national communication network with national census data on the socioeconomic well-being of communities. These data make possible a population-level investigation of the relation between the structure of social networks and access to socioeconomic opportunity. We find that the diversity of individuals’ relationships is strongly correlated with the economic development of communities.

The evolution of trust and cooperation between strangers: A computational model.

Social and economic exchanges often occur between strangers who cannot rely on past behavior or the prospect of future interactions to establish mutual trust. Game theorists formalize this problem as a one-shot prisoners dilemma and predict mutual noncooperation. Recent studies, however, challenge this conclusion. If the game provides an option to exit (or to refuse to play), strategies based on projection (of a players intentions) and detection (of the intentions of a stranger) can confer a cooperators advantage. Yet previous research has not found a way for these strategies to evolve from a random start or to recover from invasion by aggressive strategies that feign trustworthiness. The authors use computer simulation to show how trust and cooperation between strangers can evolve without formal or informal social controls. The outcome decisively depends, however, on two structural conditions : the payoff for refusing to play, and the embeddedness of interaction. Effective norms for trusting strangers emerge locally, in exchanges between neighbors, and then diffuse through weak ties to outsiders

Chains of Cooperation: Threshold Effects in Collective Action

Granovetters threshold model of collective action shows how each new participant triggers others until the chain reaction reaches a gap in the distribution of thresholds. Hence outcomes depend on the network of social ties that channel the chain reactions. However, structural analysis is encumbered by the assumption that thresholds derive from changing marginal returns on investments in public goods. A learning-theoretic specification imposes less stringent assumptions about the rationality of the actors and is much better suited to a structural analysis. Computer simulations suggest that threshold effects may be the key to solving the coordination problem: When individual choices are contingent on participation by others, this interdependence facilitates the coordination of contributions needed to shift the bistable system from a noncooperative equilibrium to a cooperative one. Further simulations with low-density networks show that these chain reactions require bridges that link socially distant actors, supporting Granovetters case for the strength of weak ties.

Social science. Computational social science.

A field is emerging that leverages the capacity to collect and analyze data at a scale that may reveal patterns of individual and group behaviors.

The weakness of strong ties : Collective action failure in a highly cohesive group

Following Homans, exchange theorists have modeled informal social control as an exchange of peer approval for compliance with group obligations. The exchange model predicts higher compliance in cohesive networks with strong social ties. However, previous specifications failed to incorporate bilateral exchange of approval. Computer simulations using a Bush‐Mosteller stochastic learning model show that bilateral exchanges evolve more readily than multilateral, causing social control to flow into the maintenance of interpersonal relationships at the expense of compliance with group obligations, a structural form of the “second‐order free‐rider problem.”