Diego F. Leal

Ph.D. Candidate in Sociology at UMass - Amherst

Department of Sociology
University of Massachusetts - Amherst
200 Hicks Way, 
Thompson Hall, Office 812
Amherst, MA, 01003
dleal [at] umass [dot] edu

Sociogram Responsive image

Social Simulation and Network Analysis Repository


Fear & Greed in Network Reciprocity, Implications for Cooperation among Organizations


This is an agent-based model (ABM) I published in PLoS ONE with other collaborators. This model is based on the spatial Prisoner’s Dilemma (PD) from Nowak and May (1992). The model allows the user to understand how the gains for exploiting cooperative partners (Greed) and the cost of cooperating with exploitive partners (Fear) impact the dynamics of cooperation in a population of agents arranged on a regular lattice. The model shows that embedding exchange in networks (in this case, a 2-dimensional grid with Moore neighborhoods) generally leads Greed and Fear to have divergent, interactive, and highly nonlinear effects on cooperation at the population level. It also shows how virtual interventions to Greed and Fear are not symmetric over time.

Description of the inter-organizational data

We also test our model using an organizational network data from a list of 4,146 board members of 2,450 of the wealthiest US corporations in 2011-12, collected by William Domhoff. We drew an undirected link between any two corporations that share at least one board member in that year. This produced a single giant component of 2,400 corporations (after excluding 50 corporations that were not connected to the others), representing 98% of the original set of corporations.

Simulation program

Click here to download the simulation program I created for this paper (requires NetLogo to run).

Mathematical supplement

Click here to download mathematical appendix.


Ethnoracial Liminality and the Diffusion of Innovations among Adolescents


This agent-based model (ABM) is part of the first chapter of my dissertation "Three Essays on Network Dynamics and Liminality". The simulation program is a threshold diffusion model based on empirical data from the first wave of the Add Health data set. This ABM allows the user to understand how several strategies aimed to diffuse an innovation perform differently. Some of the strategies are based on classic network measures like betweenness centrality or degree. Others are based on the ethnoracial structure of the network. Critically, the model shows the high spreading capacity of interracial brokers (i.e. agents that connect two alters of different ethnoracial groups).

Simulation program

Click here to download: (1) the simulation program I created (requires NetLogo to run); (2) the model pseudo-code; and (3) A presentation I did at the 2017 International Network of Analytical Sociologists Conference explaining the model and its main results.

The draft of this chapter is available upon request. Please e-mail me at dleal [at] umass [dot] edu

Migration Flows in the Americas (1960-2000): Their History and Network Dynamics


This chapter is part of my dissertation "Three Essays on Network Dynamics and Liminality". In this chapter, I develop an unprecedented analysis of migration flows in the Americas between 1960 and 2000. Using novel data and state-of-the-art techniques, I harmonize bilateral migrant stock data, with geographic distance data and demographic data on total population, deaths, and births in order to estimate migration flows between 38 countries. I then provide a detailed historic account of these flows by focusing on the following migratory subsystems: Central America and the Caribbean, North America, and South America. Finally, I use network theory and novel Temporal Exponential Random Graph (TERG) models to develop and test general hypotheses about the inter-temporal dynamics of international migration networks. In this context, my inferential network analyses show that international migration flows exhibit very strong structural signatures of hierarchy at the level of triads.


Click here to access the appendix of this chapter. In the appendix you will find: (1) the code (requires R to run) to reproduce all the analyses; (2) all the necessary input data files; and (3) some interesting figures related to sensitive analyses, robustness checks, and goodness-of-fit tests.

The draft of this chapter is available upon request. Please e-mail me at dleal [at] umass [dot] edu


Replication of Prominent Simulation Work in Sociology


I developed seven replications of prominent papers that use social simulation to advance and/or test the internal consistency of prominent sociological theories. The development of these teaching materials was done under the guidance of James Kitts in the context of a Carla B. Howery Teaching Enhancement Grant. I presented these teaching materials at ASA in 2015 (see poster here). Finally, these materials were used in a summer methods course at UMass where I was a guest lecturer

The agent-based models I developed are:

  • An agent-based diffusion model on the emergence of intergroup inequality via homophily and network externalities published in AJS by Paul DiMaggio and Filiz Garip.
  • An agent-based model on the emergence of antisocial norms via rival incentives and peer pressure published in ASR by James Kitts.
  • An agent-based model on the emergence of collective action via adaptive thresholds and stochastic learning published in ASR by Michael Macy.
  • An agent-based model on the emergence of generalized exchange through an evolutionary approach published in AJS by Nobuyuki Takahashi.
  • An agent-based model on the emergence of opinion similarity via homophily and influence published in AJS by Daniel Dellaposta and colleagues.

The system-level models I developed are:

  • A model on state legitimacy and imperialist capitalism published in Sociological Methodology by Robert Hanneman and colleagues.
  • A model on the emergence of cooperation with three different strategies that evolve over time published in the Journal of Conflict Resolution by Jack Hirshleifer and Juan Carlos Martínez.


Click here to download the all simulation programs (requires NetLogo and Stella) and other relevant materials related to these models.