Equality bias impairs collective decision-making across cultures

Edited by Richard M. Shiffrin, Indiana University, Bloomington, IN, and approved February 6, 2015 (received for review November 16, 2014)
March 9, 2015
112 (12) 3835-3840

Significance

When making decisions together, we tend to give everyone an equal chance to voice their opinion. To make the best decisions, however, each opinion must be scaled according to its reliability. Using behavioral experiments and computational modelling, we tested (in Denmark, Iran, and China) the extent to which people follow this latter, normative strategy. We found that people show a strong equality bias: they weight each other’s opinion equally regardless of differences in their reliability, even when this strategy was at odds with explicit feedback or monetary incentives.

Abstract

We tend to think that everyone deserves an equal say in a debate. This seemingly innocuous assumption can be damaging when we make decisions together as part of a group. To make optimal decisions, group members should weight their differing opinions according to how competent they are relative to one another; whenever they differ in competence, an equal weighting is suboptimal. Here, we asked how people deal with individual differences in competence in the context of a collective perceptual decision-making task. We developed a metric for estimating how participants weight their partner’s opinion relative to their own and compared this weighting to an optimal benchmark. Replicated across three countries (Denmark, Iran, and China), we show that participants assigned nearly equal weights to each other’s opinions regardless of true differences in their competence—even when informed by explicit feedback about their competence gap or under monetary incentives to maximize collective accuracy. This equality bias, whereby people behave as if they are as good or as bad as their partner, is particularly costly for a group when a competence gap separates its members.

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Acknowledgments

We thank Tim Behrens for sharing the code for implementing the computational model and Christos Sideras for helping collect the data for experiment 4. This work was supported by European Research Council Starting Grant “NeuroCoDec #309865” (to B.B.), the British Academy (B.B.), the Calleva Research Centre for Evolution and Human Sciences (D.B.), the European Union Mind Bridge Project (D.B., K.O., A.R., C.D.F., and B.B.), and the Wellcome Trust (G.R.).

Supporting Information

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Information & Authors

Information

Published in

Go to Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Vol. 112 | No. 12
March 24, 2015
PubMed: 25775532

Classifications

Submission history

Published online: March 9, 2015
Published in issue: March 24, 2015

Keywords

  1. social cognition
  2. joint decision-making
  3. bias
  4. equality

Acknowledgments

We thank Tim Behrens for sharing the code for implementing the computational model and Christos Sideras for helping collect the data for experiment 4. This work was supported by European Research Council Starting Grant “NeuroCoDec #309865” (to B.B.), the British Academy (B.B.), the Calleva Research Centre for Evolution and Human Sciences (D.B.), the European Union Mind Bridge Project (D.B., K.O., A.R., C.D.F., and B.B.), and the Wellcome Trust (G.R.).

Notes

*A cross-country project coordinated by the Institute for Social Research of the University of Michigan: www.worldvaluessurvey.org/.
We did address this question by splitting our data (experiment 1) into two sessions to test whether participants moved closer toward the optimal weight over time. However, we found no statistically reliable difference between the two sessions. This could be due to participants’ stationary behavior or that our data and analysis did not have sufficient power to address the issue of learning.
This article is a PNAS Direct Submission.

Authors

Affiliations

Ali Mahmoodi
Control and Intelligent Processing Centre of Excellence, School of Electrical and Computer Engineering, College of Engineering, University of Tehran, 14395-515 Tehran, Iran;
School of Cognitive Science, Institute for Research in Fundamental Sciences, 19395-5746 Tehran, Iran;
Dan Bang
Department of Experimental Psychology, University of Oxford, Oxford OX1 3UD, United Kingdom;
Calleva Research Centre for Evolution and Human Sciences, Magdalen College, Oxford OX1 4AU, United Kingdom;
The Interacting Minds Centre, Aarhus University, 8000 Aarhus, Denmark;
Karsten Olsen
The Interacting Minds Centre, Aarhus University, 8000 Aarhus, Denmark;
Centre of Functionally Integrative Neuroscience, Aarhus University Hospital, 8000 Aarhus C, Denmark;
Yuanyuan Aimee Zhao
Department of Psychology, Peking University, Beijing 100871, China;
Zhenhao Shi
Annenberg Public Policy Center, University of Pennsylvania, Philadelphia, PA 19104-3806;
Kristina Broberg
Centre of Functionally Integrative Neuroscience, Aarhus University Hospital, 8000 Aarhus C, Denmark;
Shervin Safavi
School of Cognitive Science, Institute for Research in Fundamental Sciences, 19395-5746 Tehran, Iran;
Department of Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, 72012 Tubingen, Germany;
Shihui Han
Department of Psychology, Peking University, Beijing 100871, China;
Majid Nili Ahmadabadi
Control and Intelligent Processing Centre of Excellence, School of Electrical and Computer Engineering, College of Engineering, University of Tehran, 14395-515 Tehran, Iran;
School of Cognitive Science, Institute for Research in Fundamental Sciences, 19395-5746 Tehran, Iran;
Chris D. Frith
The Interacting Minds Centre, Aarhus University, 8000 Aarhus, Denmark;
Centre of Functionally Integrative Neuroscience, Aarhus University Hospital, 8000 Aarhus C, Denmark;
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom; and
Andreas Roepstorff
The Interacting Minds Centre, Aarhus University, 8000 Aarhus, Denmark;
Centre of Functionally Integrative Neuroscience, Aarhus University Hospital, 8000 Aarhus C, Denmark;
Geraint Rees
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom; and
Institute of Cognitive Neuroscience, University College London, London WC1N 3AR, United Kingdom
Bahador Bahrami1 [email protected]
The Interacting Minds Centre, Aarhus University, 8000 Aarhus, Denmark;
Institute of Cognitive Neuroscience, University College London, London WC1N 3AR, United Kingdom

Notes

1
To whom correspondence should be addressed. Email: [email protected].
Author contributions: A.M., D.B., K.O., C.D.F., A.R., G.R., and B.B. designed research; A.M., D.B., K.O., Y.A.Z., Z.S., K.B., S.S., S.H., and B.B. performed research; A.M., D.B., K.O., Y.A.Z., and B.B. analyzed data; and A.M., D.B., K.O., M.N.A., C.D.F., A.R., G.R., and B.B. wrote the paper.

Competing Interests

The authors declare no conflict of interest.

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    Equality bias impairs collective decision-making across cultures
    Proceedings of the National Academy of Sciences
    • Vol. 112
    • No. 12
    • pp. 3583-E1510

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