Trust constitutes an essential component of social interaction. Trust enables peaceful coexistence, simplifies and stimulates economic exchange, and fosters economic growth (Coleman, 2000; Knack and Keefer, 1997; Zak and Knack, 2001; Cox, 2008; Güth et al., 2008).
Recently however, increasing population heterogeneity (e.g. through refugee- or labour migration) has posed a challenge to societal trust. Empirical studies show a lower trust in foreigners (Alesina and Ferrara, 2000), and that people are more likely to trust others with similar characteristics (Tanis and Postmes, 2005). Group-based distrust constitutes a serious problem for both minority and majority groups, as this potentially leaves many (economic) opportunities untaken, hampers progress and contributes to deteriorating social cohesion. These problems necessitate inquiry into the causal roots of group-based distrust.
Why is it that we trust outsiders less than people ‘from our own group’? A common and immediate answer points to people’s cultural sentiments and their feeling of group-belonging that lead to group-based discrimination in matters of trust. While this paper does not dispute or excuse the persistence of any form of such sentiments, it points out a potential alternative explanation for different trust-levels based on individually rational considerations.
By means of an agent-based model, this paper explores the dynamics of trust within and between different societal groups. Simulations suggest that outgroup trust is harder to establish even if trustworthiness is constant across groups. This stems from a seemingly minor asymmetry in learning when people conditionalise their beliefs about trustworthiness on group membership: While trustors directly learn about the trustworthiness of members of any group, inferences as a trustee allow one to draw conclusions about one’s in-group only.
This insight has far-reaching implications for how to deal with outgroup distrust. While cultural sentiments would require to overcome lack of trust between groups, distrust stemming from the described learning asymmetries must be addressed differently. This knowledge can be used to inform policies aimed at creating and sustaining social cohesion, which have received broad attention in current public discussion.
Apart from the model’s high practical relevance, it also provides a platform to discuss some important issues in the philosophy of simple models. A common view in the field is that simple models (only) provide ‘how-possibly’ explanations, as long as they lack further empirical embedding (Reutlinger et al 2016, Fumagalli 2016). Without disputing this claim, this paper argues that minimalist models can nonetheless be highly relevant as consistency checks for competing ‘how-actually’ explanations and can help to identify hidden mechanisms that may be inherent to empirically verified explanations of certain phenomena.
The provided trust model for example shows that categorisation alone is sufficient to generate non-justified discrimination. As categorisation is a component of virtually all offered ‘how-actually’ explanations of out-group distrust, the described asymmetric-learning mechanism may contribute to producing out-group discrimination parallel to these mechanisms. This would be very hard to discover empirically. The second meta-implication that can be derived from the model concerns the nature and scope of rationality. As this paper reminds us, a thin notion of rationality that envisages preferences and beliefs as fixed and separate entities from an individual’s utility maximising actions falls short in capturing potential feedback loops from actions to beliefs. In the context of the model, choosing not to trust a certain individual because of her group-membership not only influences the payoffs one earns, but also what information one will be receiving in the future.
Third, the point that ‘categorisation itself matters’ illustrates that a problem’s conceptualisation already determines how the problem is solved to some extent. An agent who envisages trustworthiness as a potentially group-specific feature will draw different conclusions than an agent who does not see the problem that way. Thus, whether or not one should distinguish according to various salient group-characteristics is itself a rational decision to be made by the agent.
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