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Even arbitrary norms influence moral decision-making


It is well known that individuals tend to copy behaviours that are common among other people—a phenomenon known as the descriptive norm effect1,2,3. This effect has been successfully used to encourage a range of real-world prosocial decisions4,5,6,7, such as increasing organ donor registrations8. However, it is still unclear why it occurs. Here, we show that people conform to social norms, even when they understand that the norms in question are arbitrary and do not reflect the actual preferences of other people. These results hold across multiple contexts and when controlling for confounds such as anchoring or mere-exposure effects. Moreover, we demonstrate that the degree to which participants conform to an arbitrary norm is determined by the degree to which they self-identify with the group that exhibits the norm. Two prominent explanations of norm adherence—the informational and social sanction accounts2,9,10,11—cannot explain these results, suggesting that these theories need to be supplemented by an additional mechanism that takes into account self-identity.

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Fig. 1: Effect of arbitrary norms in experiments 1a and 1b.
Fig. 2: Effect of arbitrary norms that refer to which option is unpopular.
Fig. 3: Effect of unrelated arbitrary norms.
Fig. 4: Effect of arbitrary norms when both an in-group and out-group norm are presented.

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Data availability

The response data for all pilot experiments and experiments in this paper are available in the following OSF repository:


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This research was supported by an Australian Government Research Training Program Scholarship. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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All authors contributed to the study design. Testing, data collection and analysis were performed by C.P. under the supervision of P.D.L.H. and A.P. C.P. drafted the manuscript, and P.D.L.H. and A.P. provided critical revisions. All authors approved the final version of the manuscript for submission.

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Correspondence to Piers D. L. Howe.

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Pryor, C., Perfors, A. & Howe, P.D.L. Even arbitrary norms influence moral decision-making. Nat Hum Behav 3, 57–62 (2019).

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