Agent-based modeling
Agent-based modeling (ABM) is rapidly gaining in popularity as a tool for the development and refinement of theoretical models. While game-theoretic modeling permits rigorous and precise analysis, this is only possible for models that are drastically simplified. Almost any attempt to introduce more realistic assumptions into such models, or to introduce more than just two or three actors, almost inevitably makes them analytically intractable. Computer simulations, in contrast, allow us to investigate systematically and exhaustively the implications of changes in the independent variables, including preferences and identities, for any number of actors.
From a more practical pont of view, ABM allows us to run our own quasi-experiments when the real world does not provide enough data. Moreover, it allows us to investigate whether the stated assumptions and parameters of a model can (and will) produce the outcomes that we theoretically predict or empirically observe.
In my own ABM research, I examine the micro-foundations of identity and preference change, with obvious implications for the empirical research questions listed in the other sections on this page.
We still have much to learn regarding the diffusion of ideas and identities. For example, how does the social connectedness of a polity affect such a diffusion? Is it easier for ideas to spread in very hierarchical societies? Or in societies where social connections are far-flung rather than predominantly local? The nature of a particular idea or identity is also likely to have an impact. We might expect it to be difficult for incompatible ideas to co-exist or spread, but as the White Queen says in Alice in Wonderland: "I've believed as many as six impossible things before breakfast."
The questions become even more interesting — and complex to model — once we include material factors into the equation. Identities are likely to spread more easily when there are political rewards for adopting (or expressing) a particular identity, for example. Certain norms may have a difficult time spreading through a population if living up to those norms carries an economic cost. Conversely, norms or other ideas may be able to piggy-back on successful economic transactions. Each of these questions, though framed in an abstract manner, has obvious relevance to some very important real-world issues: When might political entrepreneurs benefit from trying to recruit followers by appealing to ethnic divisions? Will more internal trade facilitate the emergence of a European identity in the EU? Etcetera.
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The Emergence of a Shared Identity: An Agent-Based Computer Simulation of Idea Diffusion
Liberal theorists and, more recently, constructivists have argued that a shared sense of identity will
decrease threat perception and increase international cooperation. But what processes lead to the emergence
(or collapse) of a shared sense of identity? Drawing on individual-level experiments of identity change and
societal-level theories of idea diffusion from the constructivist literature, the authors develop an agent-based
computer simulation of identity change. Four findings emerge from the analysis: (1) there is a curvilinear
relationship between the complexity of agentsÕviews and the emergence of shared identity, (2) highly unstable
environments encourage the emergence of a shared identity, (3) the presence of leaders (i.e., agents with
greater influence in the population) in the neighborhood decreases shared identity, and (4) the interaction of
complexity, stability, and leadership produces extremely polarized societies.
(Click to download a copy of the article)
David L. Rousseau,
A. Maurits van der Veen
Journal of Conflict Resolution 49(5):686-712. October 2005.
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Modeling the Evolution of Ethnic Demography
We develop an agent-based model that allows us to study the dynamics of ethnic demography. Identities are modeled as constructed from a repertoire of identity attributes, which vary in the degree to which they are sticky (i.e. easy to drop or change). Individual agents can change their identity repertoire over time, within the constraints of stickyness, and they can also choose to highlight particular components of their repertoire. Political leaders propose coalitions in the form of certain identity conditions, so that only those who meet those conditions (have the correct attributes in their repertoire) can join. The model is then used to investigate under what conditions electoral institutions have the same impact on leadership stability in countries where ethnic cleavages dominate and in countries politically divided on less "sticky" dimensions.
(Click to email me for a copy of the paper)
A. Maurits van der Veen,
David D. Laitin
Prepared for inclusion in an edited volume on the political economy of ethnicity, edited by
Kanchan Chandra.
In process.
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Ethnicity and Pork: A Virtual Test of Causal Mechanisms
We use an agent-based model of the dynamics of ethnic demography (see immediately above) to investigate the widely recognized elective affinity between ethnicity and the exclusionary distribution of political benefits, also known as "pork". We show that when political entrepreneurs have incentives to seek small coalitions (due to the goal of distributing a limited amount of pork to supporters), those that win and stay in power are those that attract voters based on their ethnic membership. Moreover, our findings elucidate the mechanisms that drive political entrepreneurs to propose and voters to support ethnic coalitions when distribution (i.e. pork) rather than policy drives political competition. In particular, we show that an affinity between ethnicity and pork emerges even when neither the public nor its leaders consciously takes into account differences between ethnic identities and other forms of political identification. Finally, the affinity between ethnicity and pork applies not just to winning coalitions, but also to the overall nature of political contestation: If pork is up for grabs, ethnic identities become more politically salient.
(Click to email me for a copy of the paper)
David D. Laitin,
A. Maurits van der Veen
Prepared for inclusion in an edited volume on the political economy of ethnicity, edited by
Kanchan Chandra.
In process.
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Studying Performance and Learning with ABIR: The Effects of Knowledge, Mobilizing Agents, and Predictability
We use the Agent-Based Identity Repertoire model to investigate the ability of populations to adapt and learn in an unpredictable environment. Our findings highlight the trade-off between adaptation and diversity in the pursuit of performance, but also show that this trade-off is far from straight-forward. Increasing sophistication improves the ability to adapt but reduces diversity, imposing high costs down the line. However, high levels of sophistication also produce small, stable homogeneous clusters of agents, which slow down declines in diversity. Innovative or entrepreneurial agents reacting more rapidly to environmental signals increase the prevalence of such clusters, helping diversity but hampering adaptability. This makes it difficult to improve performance systematically by introducing such agents into a population. We also show that more predictable environments facilitate successful adaptation, especially for populations of intermediate sophistication. Finally, we conclude that the trade-off between adaptation and diversity is such that, in the present model, long-term learning is difficult to achieve
(Click to download a preprint copy of the article)
A. Maurits van der Veen,
Ian S. Lustick,
Dan Miodownik
Social Science Computer Review 19(3):263-279. Fall 2001.
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Transforming the Prisoner's Dilemma: Beyond One-Dimensional Utility Functions
It is well-known that cooperation can evolve and be sustained among populations playing iterated prisoner's dilemmas, as long as the shadow of the future is sufficiently large. An extensive literature has arisen examining ways to lengthen that shadow, for example by introducing local context preservation or tagging of agents. Comparatively less attention has been paid to the possibility of changing the utility functions of the agents themselves. The present paper is a first attempt at investigating the implications of doing so. The experiments presented here show that allowing agents to derive utility from conformity or loyalty, and particularly from normatively cooperative behaviour, greatly facilitates the emergence of cooperation, in situations where traditional payoffs alone prevent such an outcome.
(Click to email me for a copy of the paper)
Presented at the annual conference of the American Political Science Association, Boston, August 2008.
In process.
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The Emergence of a European Identity: Modeling International Contacts
This paper uses agent-based modeling to study the role of different variables in the emergence and spread of a European identity. I investigate the impact of two different types of international contacts on the spread of a European identity: exchange programs and social networks among leaders. The results illustrate how difficult it is for a strong sense of European identity to emerge. More specifically, I find that foreign study programs do not contribute to the spread of a European identity — instead, it seems likely that those who feel European are more likely to study abroad. In addition, although a network of political elites that lacks international contacts strongly favours the national identity, the converse fails to hold: an international network of elites does little to improve the fortunes of the European identity.
(Click to email me for a copy of the paper)
Presented at the annual conference of the American Political Science Association, Philadelphia, August 2003.
In process.
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