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Credibility-enhancing displays promote the provision of non-normative public goods


Promoting the adoption of public goods that are not yet widely accepted is particularly challenging. This is because most tools for increasing cooperation—such as reputation concerns1 and information about social norms2—are typically effective only for behaviours that are commonly practiced, or at least generally agreed upon as being desirable. Here we examine how advocates can successfully promote non-normative (that is, rare or unpopular) public goods. We do so by applying the cultural evolutionary theory of credibility-enhancing displays3, which argues that beliefs are spread more effectively by actions than by words alone—because actions provide information about the actor’s true beliefs. Based on this logic, people who themselves engage in a given behaviour will be more effective advocates for that behaviour than people who merely extol its virtues—specifically because engaging in a behaviour credibly signals a belief in its value. As predicted, a field study of a programme that promotes residential solar panel installation in 58 towns in the United States—comprising 1.4 million residents in total—found that community organizers who themselves installed through the programme recruited 62.8% more residents to install solar panels than community organizers who did not. This effect was replicated in three pre-registered randomized survey experiments (total n = 1,805). These experiments also support the theoretical prediction that this effect is specifically driven by subjects’ beliefs about what the community organizer believes about solar panels (that is, second-order beliefs), and demonstrate generalizability to four other highly non-normative behaviours. Our findings shed light on how to spread non-normative prosocial behaviours, offer an empirical demonstration of credibility-enhancing displays and have substantial implications for practitioners and policy-makers.

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Fig. 1: Ambassadors who install solar panels through the Solarize programme are more successful at convincing others to participate than ambassadors who do not.
Fig. 2: Ambassador installation influences subjects’ intentions to install through the Solarize programme.
Fig. 3: Second-order beliefs explain the effect of ambassador installation on the installation intentions of subjects.
Fig. 4: Ambassador engagement promotes contribution to highly non-normative public goods.

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This research was made possible by US Department of Energy (award DE-EE0006128), the Templeton World Charity Foundation (grant no. TWCF0209) and the Defense Advanced Research Projects Agency NGS2 programme (grant no. D17AC00005). The authors thank S. Carattini, C. Moya and M. Hoffman for their helpful feedback on drafts of this manuscript, and D. Banko and C. Borden for research assistance.

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Nature thanks A. Grønhøj, L. Stanca and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Authors and Affiliations



K.G. and B.B. designed and conducted the field study. G.T.K.-T. and S.L. analysed the results of the field study. G.T.K.-T. and D.G.R. designed the online experiments. G.T.K.-T. conducted the online experiments and analysed the results. G.T.K.-T., B.B., K.G., S.L. and D.G.R. wrote the paper.

Corresponding authors

Correspondence to Gordon T. Kraft-Todd or David G. Rand.

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The authors declare no competing interests.

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Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Results of the norming study regarding injunctive norms.

Distributions are shown of subjects’ (n = 100) responses to the question: ‘in your opinion, how much do people in your community think doing this behaviour is what you are supposed to do?’. Responses were given on a Likert scale between 1 (‘very little’) and 7 (‘very much’).

Extended Data Fig. 2 Results of the norming study regarding descriptive norms.

Distributions are shown of subjects’ (n = 100) responses to the question: ‘in your opinion, how many people in your community do this behaviour?’. Responses were given on a Likert scale between 1 (‘very few’) and 7 (‘very many’).

Extended Data Fig. 3 Example photographs from Solarize campaigns.

ac, A live installation event (a), a campaign kick-off event (b) and flyers and signs for an informational event (c) are shown. Photographs courtesy of SmartPower.

Extended Data Fig. 4 Mediation analysis for experiment 3.

Because there is no evidence of heterogeneity in the effect of CREDs across non-normative public-good scenarios, we collapse across scenario (total n = 1,206) and see that subjects’ second-order beliefs fully mediate the effect of ambassador engagement on subject intentions to engage in the behaviour in question. All variables are standardized for this analysis. The correlations between ambassador engagement and second-order beliefs, second-order beliefs and subjects’ intentions to engage in the behaviour, and ambassador engagement and subjects’ intentions to engage in the behaviour (without (b) and with (b′) second-order beliefs as a covariate) are shown.

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Kraft-Todd, G.T., Bollinger, B., Gillingham, K. et al. Credibility-enhancing displays promote the provision of non-normative public goods. Nature 563, 245–248 (2018).

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