Groups and conflict

• Hirotaka Imada, Rebecca Kopilovitch and Ro'i Zultan (2025). Ingroup favoritism in cooperation in a dynamic intergroup context: data from Israeli professional volleyball players. Judgment and Decision Making, 20, e21. [PDF] [DOI]
  The two leading explanations for in-group cooperation are social identity theory (SIT) and bounded generalized reciprocity (BGR). These theories have differential predictions for cooperation with members of groups one no longer belongs to. SIT predicts high levels of cooperation as long as the individual identifies with her past group, while BGR predicts no effect for past affiliation regardless of identification. We tested these predictions with professional vollleyball players. We find high levels of identification and cooperation with in-group members. Although players identify with their past teams, cooperation levels are the same as with a neutral team.
• Ori Weisel and Ro'i Zultan (2021). Perceptions of conflict: Parochial cooperation and outgroup spite revisited. Organizational Behavior and Human Decision Processes, 167, 57–71. [PDF] [DOI]
  In Weisel and Zultan (2016), we showed that behavior in conflict crucially depends on the perception of the level of threat. Here, we extend this insight to motives in participation in conflict. We replicate the common finding that people are motivated to help their ingroup rather than to harm their outgroup. We should that this result is restricted to situations were the perceived level of threat is the individual. When we shift the perception to the group level, people are willing to harm the outgroup.
• Ori Weisel and Ro'i Zultan (2021). Perceived level of threat and cooperation. Frontiers in Psychology, 12, 704338. [PDF] [DOI]
  An opinion piece, in which we review evidence for the perceived level of threat principle.
• David Hugh-Jones, Itay Ron and Ro'i Zultan (2019). Humans reciprocate by discriminating against group peers. Evolution and Human Behavior, 40(1) 90–95. [PDF] [DOI]
  We conducted a controlled experiment to test the hypothesis that humans practice group reciprocity: they reciprocate the actions of one individual towards unrelated individuals belonging to the perpetrator's group. We find evidence for group reciprocity only when the initial action is unambiguously intentional.
• Ori Weisel and Ro'i Zultan (2016). Social Motives in Intergroup Conflict: Group Identity and Perceived Target of Threat. European Economic Review, 90, 122–133. [PDF] [DOI]
  We study the effects of intergroup conflict on group identity and cooperation. We find that conflict affects behavior only through the perception of threat. Perception of threat to the group triggers group identity and cooperation. When the same threat is perceived as threat to the individual, it triggers selfish motives and reduces cooperation.
• David Hugh-Jones and Ro'i Zultan (2013). Reputation and Cooperation in Defence. Journal of Conflict Resolution, 57(2), 364–392. [PDF] [DOI]
  An outside threat increases in-group cooperation. We provide a game-theoretical and evolutionary explanation for the effect based on group reputation.

Ethics and ethical decision making

• Shlomo Cohen and Ro'i Zultan (2021). The Deceiving Game. Journal of the American Philosophical Association, 7(4), 439–452. [PDF] [DOI]
  Are lies morally worse than other modes of deception? We develop four normative arguments for why this is the case, and show that each argument rests on an empirically testable assumption, which we test in two experiments. Thus, we provide empirical evidence for a normative debate without falling prey to the naturalistic fallacy.
• Shlomo Cohen and Ro'i Zultan (2022). Genomic Privacy, Identity, and Dignity. Journal of Medical Ethics, 48, 317–322. [PDF] [DOI]
  The notion that genomic information is inherently private provides a basis to object to public biobanks, even if any harmful consequences can be averted. We test to what extent people perceive exposure of genomic information to be a violation of privacy. We find that, in comparison to other non-consequentialist privacy interests, concerns for genomic privacy are rather weak.
• Sigal Vainapel, Ori Weisel, Ro'i Zultan and Shaul Shalvi (2019). Group moral discount: diffusing blame when judging group members. Journal of Behavioral Decision Making, 32(2), 212–228. [DOI]
  Athough groups tend to lie more than individuals, people do not suspect groups more they do individuals. However, when the group acted in a suspicious way, group members are less likely to be suspected, judged negatively, punished, and reported on, when they are judged as separate individuals compared with as a group.
• Ivan Soraperra, Ori Weisel, Ro’i Zultan, Sys Kochavi, Margarita Leib, Hadar Shalev, and Shaul Shalvi (2017). The bad consequences of teamwork. Economic Letters, 160, 12–15. [PDF][DOI]
  People cheat more as part of a collaborative effort. We explore two possible explanations. One, that people are exposed in collaboration to corrupt norms, and two, that collaboration is perceived as an ethical activity, so that cheating in collaboration is not perceived as unethical. We compared treatments in which cheating is either done in collaboration with, or merely observed by the partner. Overall dishonesty levels are similar across the two treatments, but collaboration results in fewer dyads where both partners behave honestly.

Markets and auctions

• Lawrence Choo, Todd R. Kaplan and Ro'i Zultan (2022). Manipulation and (Mis)trust in Prediction Markets. Management Science, 68(9). 6716–6732. [PDF] [DOI]
  Governments and firms increasingly use prediction markets to guide policy and strategic decisions. If prices affect decision making, the market is no longer self contained, and manipulators with a vested interest are able to inject money into the market in order to manipulate prices. In our experiment, we find that uncertainty regarding manipulation harms information aggregation, even if there is no actual manipulation. Manipulators are able to substantially impede information aggregation. Importantly, decision makers are still able to benefit from following the market, but refrain from doing so because manipulation endangers distrust.
• Sven Fischer, Werner Güth, Todd R. Kaplan and Ro'i Zultan (2021). Auctions and Leaks: A Theoretical and Experimental Investigation. Economic Inquiry, 59(2), 722–739. [PDF] [DOI]
  We analyze bidding when the bid of one bidder may be revealed to the other bidder. We characterize the equilibria in first-price auctions with risk aversion and show experimentally that behavior is consistent with the equilibrium prediction. Multiple equilibria exist in second-price auction. We identify three focal equilibria and show that (a) these equilibria account for most of the data, and (b) there is individual consistency in equilibrium selection. Behavior and outcomes are, on average, similar to the no-leaks baseline.
• Lawrence Choo, Todd R. Kaplan and Roi Zultan (2019). Information Aggregation in Arrow-Debreu Markets: An Experiment. Experimental Economics, 22(3), 625–652. [PDF] [DOI]
  We test the ability of markets to successfully aggregate dispersed information into prices. We find that, if traders are experiences, prices reflect the true state even when all traders hold the same initial beliefs over the values of the traded assets. When some traders hold better initial information, these traders are better informed and are instrumental in driving prices to equilibrium, but are not able to obtain higher profits. Finally, prices reflect the true state even though the traders by and large remain uninformed.
• Aniol Llorente-Saguer and Ro'i Zultan (2017). Collusion and Information Revelation in Auctions. European Economic Review, 95, 84–102. [PDF] [DOI]
  We show that first-price auctions lead to worse outcomes than second-price auctions under collusion. This counters existing theoretical results, which do not consider the implications of failed collusive negotiations for bidding behavior.

Labor economics

• Oded Ravid, Miki Malul and Ro'i Zultan (2021). Incentives, Mission and Productivity. Journal of Behavioral and Experimental Economics, 101668. [PDF] [DOI]
  High-power incentives in the private sector lead to high productivity both by attracting high-ability workers from the public sector and by incentivizing high effort. These sorting and incentivizing effects lead to a productivity gap between the two sectors. In a controlled laboratory experiment, we replicate the productivity gap. When work in the public sector generates a public good—captured in the experiment by donations to charity—the emerging sense of mission mitigates both the sorting and the incentivizing effect while maintaining the relative contribution of each to the productivity gap.
• Tomer Blumkin, Haim Pinhas and Ro'i Zultan (2020). Wage Subsidies and Fair Wages. European Economic Review, 127, 103497. [PDF] [DOI]
  Wage subsidies can be paid directly to workers or indirectly by subsidizing employers' wage costs. We propose that indirect subsidies are perceived by workers as contributing to fair wages, motivating them to voluntarily increase productivity. Thus, indirect subsidies lead to higher social welfare for the same government expenditure.
• Andriy Zapechelnyuk and Ro'i Zultan (2020). Job Search Costs and Incentives. Economic Theory Bulletin, 8, 181–202. [PDF] [DOI]
  Making jobs easier to find can improve job market efficiency. In an environment of fixed contracts and moral hazard, however, some individuals may be incentivized to shirk on the job at the cost of being fired and having to find a new job. This leads to an overall reduction of productivity and wages in the market and a loss of social welfare.
• Oded Ravid, Miki Malul and Ro'i Zultan (2017). The Effect of Economic Cycles on Job Satisfaction in a Two-Sector Economy. Journal of Economic Behavior & Organization, 138, 1–9. [PDF] [DOI]
  In the public sector, compensation and job security are less sensitive to economic cycles than in the private sector. Because subjective wellbeing, including job satisfaction, responds to relative comparisons, we hypothesize that job satisfaction in the public sector is countercyclical. This hypothesis was borne out in a controlled laboratory experiment simulating a two-sector economy.
• Esteban Klor, Sebastian Kube, Eyal Winter and Ro'i Zultan (2014). Can Higher Rewards Lead to Less Effort? Incentive Reversal in Teams. Journal of Economic Behavior & Organization, 97, 72–83. [PDF] [DOI]
  We show in two experiments that increasing team bonuses (or equivalently reducing effort costs) can reduce effort due to complementarities between agents.
• Sebastian Goerg, Sebastian Kube and Ro'i Zultan (2010). Treating Equals Unequally - Incentives in Teams, Workers' Motivation and Production Technology. Journal of Labor Economics, 28, 747–772. [PDF] [DOI]
  We show experimentally that arbitrary wage discrimination can increase agents' effort by solving the coordination problem that arises under equal wages with complementarities between agents.

Cooperation

• Yamit Asulin, Yuval Heller, Nira Munichor and Ro'i Zultan (2025). Social image, observer identity, and crowding up. Games and Economic Behavior. [PDF]
  People behave more normatively when someone is watching. We contribute to the literature on social image concerns by considering the question of who is watching. We suggest that, while the opinions of friends are more important, observation by an acquaintance may have a stronger effect on behavior because the observed actions are more likely to move the acquaintance's beliefs. We conducted a field experiment with high school students to find that observation by an acquaintance has a stronger effect on young adolescents but not on the older participants.
• Sagi Dekel, Sven Fischer and Ro'i Zultan (2017). Potential Pareto Public Goods. Journal of Public Economics, 146, 87–96. [PDF] [DOI]
  Potential Pareto Public Goods create an aggregate benefit to society while harming some members of the community. We find that contributions to Potential Pareto Public Goods are not viewed as unequivocally socially desirable and do not increase with communication or punishment. When it is possible to compensate the harmed parties, communication facilitates compensation. Consequently, contributions are no longer viewed as socially undesirable, and majority contributions increase.
• Eva-Maria Steiger and Ro'i Zultan (2014). See No Evil: Information Chains and Reciprocity. Journal of Public Economics, 109, 1–12. [PDF] [DOI]
  Being observed leads people to increase their effort in anticipation of positive reciprocity. Observing others increases the chance of observing a shirker and negatively reciprocating by shirking. Partial transparency, in which individuals only observe the previous mover leads to the highest effort.
• M. Vittoria Levati and Ro'i Zultan (2011). Cycles of Conditional Cooperation in a Real-Time Voluntary Contribution Mechanism. Games, 2(1), 1–15. [PDF] [DOI]
  We develop a measure of conditional cooperation in a real-time contribution setting.

Responsibility in teams

• Tobias Gerstenberg, David Lagnado and Ro'i Zultan (2023). Making a poitive difference: criticality in groups. Cognition, 238, 105499. [PDF][DOI]
  We test five models of ex-ante responsibility. Anticipated pivotality for positive outcomes emerges as the model best explaining criticality attributions.
• David Lagnado, Tobias Gerstenberg and Ro'i Zultan (2013). Causal responsibility and counterfactuals. Cognitive Science, 37(6), 1036–1073. [DOI]
  We develop and test a framework for assigning responsibility in teams. Ex-post responsibility is a function of ex-ante criticality and ex-post counterfactual pivotality.
• Ro'i Zultan, Tobias Gerstenberg and David Lagnado (2012). Finding Fault: Causality and Counterfactuals in Group Attributions. Cognition, 125, 429–440. [PDF] [DOI]
  We show that, consistent with counterfactual causal reasoning, blame assigned to a team member increases (decreases) with the performance of complementing (substitute) peers.

Game theory

• M. Vittoria Levati, Matthias Uhl and Ro'i Zultan (2014). Imperfect Recall and Time Inconsistencies: An experimental test of the absentminded driver "paradox". International Journal of Game Theory, 43, 65–88. [PDF] [DOI]
  Piccione and Rubinstein (1997) argued that the optimal strategy of absentminded decision makers may change over time even in the absence of any new information. We provide supporting experimental results.
• Ro'i Zultan (2013). Timing of Messages and the Aumann Conjecture: A multiple-Selves Approach. International Journal of Game Theory, 42, 789–800. [PDF] [DOI]
  Does it matter whether people send a message about intentions or about actions? I show that the puzzling experimental results of Charness (2000) can be rationalized if the formal modelling of the game separates the action and the message.

Communication and cooperation

• Ro'i Zultan (2012). Strategic and Social Pre-Play Communication in the Ultimatum Game. Journal of Economic Psychology 33(3), 425–434. [PDF][DOI]

  I show that strategic and pure social communication lead to similar outcomes—but working through different channels.

• Ben Greiner, Werner Güth and Ro'i Zultan (2012). Social Communication and Discrimination: A Video Experiment. Experimental Economics, 15(3), 398–417. [PDF] [DOI]
  Mere exposure to others doesn't increase generosity. We find that although there is no effect on average, there are idiosyncratic effects based on impression formation. We establish causality using video technology.
• Carsten Schmidt and Ro'i Zultan (2005). The Uncontrolled Social Utility Hypothesis Revisited. Economics Bulletin 3, 1–7. [PDF]
  Preliminary results disentangling strategic and pure social communication.

Judgment and decision making

• Ro'i Zultan, Ori Weisel and Yaniv Shani (2025). Acting Wastefully but Feeling Satisfied: Understanding Waste Aversion. Journal of Behavioral Decision Making, 38(2), e70011. [PDF][DOI]
  We show that people are happier with, and are willing to extend search wastefully in order to obtain a wasteful outcome that eliminates feelings of wastefulness. This effect exists independent of feelings of regret.
• Ya'akov Bayer, Bradley J. Ruffle, Ze'ev Shtudiner and Ro'i Zultan (2018). Costly Superstitious Beliefs: Experimental Evidence. Journal of Economic Psychology, 69, 30–43. [DOI]
  We show the effect of superstitious beliefs on economic decision making. Acoording to a common Israeli popular belief, it is bad luck to furnish an unborn child's room. We elicit pregnant women's cash equivalence of a children furniture voucher. Whether the furniture has to be installed before the expected birth influenced choices. Women who rated higher on a popular belief scale attached a lower value to the furniture.
• Ro'i Zultan, Maya Bar-Hillel and Nitsan Guy (2010). When Being Wasteful Is Better than Feeling Wasteful. Judgment and Decision Making, 5(7), 489–496. [PDF]
  Paying a fixed price for a service can be ex-post wasteful if it turns out that the required service would have been cheaper on a per-use basis.