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Edited by Richard M. Shiffrin, Indiana University, Bloomington, IN, and approved February 6, 2015 (received for review November 16, 2014)
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.
Footnotes
- ↵1To whom correspondence should be addressed. Email: bbahrami{at}ucl.ac.uk.
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.
The authors declare no conflict of interest.
*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.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1421692112/-/DCSupplemental.
Equality bias in joint decisions
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