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Random deviations and the micro-macro-problem

Michael Mäs, ETH Zurich

Economic and psychological research has led to significant improvements in our theories of human behavior. Yet, a considerable part of individuals’ behavior remains unexplained as it unpredictably deviates from the predictions of our theories. In this talk, I argue that our explanations of collective phenomena need to take into account these micro-level deviations. In fact, I show that even a theory that perfectly captures all individual-level patterns may fail to explain collective phenomena if these deviations are not taken into account.

I study this problem in the contexts of cultural differentiation, and coordination in networks. The presentation consists of three parts. I first show that existing macro models fail to explain patterns of cultural diversity when random deviations from the core micro-assumptions are included.

Second, I show that random processes may also generate and stabilize macro-patterns that appear to be difficult to explain with deterministic assumptions about individual behavior.

Third, I present results from a laboratory experiment which tested the hypothesis that deviations at the micro-level can drastically affect collective dynamics. Our empirical results support the notion that in social networks small deviations at the individual level can spark behavioral cascades that critically shape the structure of the collective level.

I conclude that making deterministic assumptions about the behavior of individuals can lead to fundamentally wrong macro-predictions. Second, future research should identify the conditions under which social systems are stochastically unstable in the sense that deviations can have decisive impact on macro-level dynamics, even when deviations are rare and random.

Värdar för seminariet är Peter Hedström, David Sumpter och Fredrik Liljeros från Institutet för Framtidsstudier. Seminariet är gratis och äger rum kl. 12.30–14.00 på Institutet för Framtidsstudier, Holländargatan 13, Stockholm.

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