Coping with Heterogeneous Opinions (CHOp)

Table of Contents

The CHOp research project is funded by the ANR (ANR-17-CE26-0003) and involves three partners: THEMA–University of Cergy-Pontoise, LPC–Aix-Marseille University, and Paris School of Economics. It stated in October 2017 for a duration of 4 years. The project coordinator is Eric Danan.

Project Summary

This project tackles the issue of the diversity of opinions in a society. It is grounded in Economics but is at the intersection with several other fields: Psychology, Statistics, Decision Theory, Analytical Philosophy, Social Choice, and Political Science. It goes beyond equating individuals’ opinions with their probabilistic beliefs, a standard practice in Economics, and aims at encompassing notions like unawareness, ambiguity, and competence to analyze opinion heterogeneity more broadly. The general questions we will explore are the following ones:

  • How does diversity of opinions come about and how can it survive?
  • What is the impact of this diversity on economic arrangements?
  • How do individuals react when confronted with other’s opinions?
  • How can one aggregate the various opinions to make the best decisions?

These questions deserve to be treated both normatively and positively, calling for various analytical approaches (e.g. axiomatic treatment, modelling of markets, etc.) and experimental approaches (from psychophysics and social psychology). From a positive side, we will provide models explaining how individuals exposed to the same information can disagree. This requires to think outside of the usual Bayesian, common prior framework. Getting outside of this framework is also required to provide an understanding of how disagreements can survive in the long run, as we aim to show, contrary to a long-standing view in economics that “irrational” opinions get wiped out of the market. Experimentally, we will focus on how individuals integrate heterogeneous opinions when making decisions and, in particular, how social pressure affects individuals’ opinions. We will finally analyze how opinion heterogeneity affects economic arrangements such as bargaining, risk sharing and financial markets, incentive provision, etc.

From a normative side, we will concentrate on the many ways different opinions can be aggregated to form a social or group opinion. A particular attention will be given to procedures that allow one to extract a measure of competence or expertise from opinions expressed by members of a society or group. These degrees of competence will then be used to weight the various opinions in order to make the best informed decision for the group. We will provide an experimental assessment of these rules, compared with other rules studied in the literature. We will also go beyond taking opinions as exogenous and will see how correlations (and, possibly, failure to recognize these) among the sources of information accessible to individuals changes the way aggregating procedures like voting work. This study will fit into a more general research question which is how to aggregate “ill-defined” or “biased” opinions.

Research Team



  1. Davranche K., Carbonnell L., Belletier C., Vidal F., Huguet P., Gajdos T., Hasbroucq, T., A Simon-like effect in Go/No-Go tasks performed in isolation, Psychonomic Bulletin & Review, 2018.
  2. Dietrich F., A theory of Bayesian groups, Noûs, forthcoming.

Working papers

  1. Billot A., Qu X., Utilitarian Aggregation with Reasonably Heterogeneous Beliefs.
  2. Bouacida E., Eliciting Choice Correspondences - A General Method and an Experimental Implementation.
  3. Colo P., The IPCC in Climate Change Agreements.
  4. Colo P., What’s the Science? Communication under Model Uncertainty.
  5. Couanau Q., Robust Irreversible Investment: Competition Matters.
  6. Danan E., Partial utilitarianism.
  7. Danan E., Gajdos T., Tallon J.-M., Tailored recommendations.
  8. Davranche K., Belletier B., Gajdos T., Carbonnell L., Vidal F., Huguet P., Hasbroucq T., Deciphering the nature of the joint Simon effect through electromyographic analyses.
  9. Dietrich F., Fully Bayesian Aggregation.
  10. Dietrich F., Jabarian B., Decision under normative uncertainty.
  11. Dietrich F., List C., The relation between degrees of belief and binary beliefs: A general impossibility theorem.
  12. Ding H., Aubert C., Voter conformism and inefficient policies.
  13. Ding H., Pivato M., Does deliberation improve the reliability of epistemic democracy?.
  14. Fleurbaey M., Zuber S., Fair Utilitarianism.
  15. de Gardelle V., Nerdrum L., Vergnaud J.-C., The meaning of confidence when receiving advice.
  16. Grant S., Guerdjikova A., Quiggin J., Ambiguity and awareness: a coherent multiple priors model.
  17. Guerdjikova A, Quiggin J., Heuristic Modes of Decision Making and Survival in Financial Markets.
  18. Macé A., Treibich R., On the Weight of Sovereign Nations.
  19. Minardi S., Savotchkin A., Time for memorable consumption.
  20. Mongin P., Pivato M., Social Preference Under Twofold Uncertainty.
  21. Mukerji S., Ozsoylev H., Tallon J.-M., Trading Ambiguity: A Tale of Two Heterogeneities.
  22. Pivato M., Rank-additive population ethics.
  23. Pivato M., Soh A., Weighted representative democracy.
  24. Qu X., Belief-Consistent-Pareto Dominance.


Fisrt Internal Workshop, PSE, December 15, 2017

Location: PSE, room R6-60 (directions).


DBAED Conference, ENS, May 30-June 1, 2018

Second Internal Workshop, PSE, November 30, 2018

Location: PSE, room R5-10 (directions).


RUD 2019 Conference, PSE, June 5-7, 2019

DBAED II Conference, UCP, June 11-13, 2019