Published and forthcoming papers

Nastiness in Groups (NEW!)
Journal of the European Economic Association, 2024, forthcoming.
with Michal Bauer, Dagmara Celik Katreniak, Julie Chytilová, Lubomír Cingl, and Tomáš Želinský
This paper provides evidence showing that people are more prone to engage in nasty behavior, malevolently causing financial harm to other people at own costs, when they make decisions in a group context rather than when making choices individually on their own. We establish this behavioral regularity in a series of large-scale experiments among university students, adolescents, and nationally representative samples of adults — more than ten thousand subjects in total. We test several potential mechanisms, and the results suggest that individual nasty inclinations are systematically more likely to affect behavior when decisions are made under the “cover” of a group, i.e., in a group decision-context that creates a perception of diffused responsibility.

Can you spot a scam? Measuring and improving scam identification ability (NEW!)
Journal of Development Economics, 2023, 165, 103147. 
with Elif Kubilay ⓡ Eva Raiber ⓡ Lisa Spantig ⓡ Lucy Kaaria 
The recent expansion of digital financial products leads to severe consumer protection issues such as fraud and scams. As these potentially decrease trust in digital services, especially in developing countries, avoiding victimization has become an important policy objective. In an online experiment, we first investigate how well individuals in Kenya identify phone scams using a novel measure of scam identification ability. We then test the effectiveness of scam education, a commonly used approach by banks and institutions for fraud and scam prevention. We find that common tips on how to spot scams do not significantly improve individuals’ scam identification ability, i.e., the distinction of scams from genuine messages. This null effect is driven by an increase in correctly identified scams and a decrease in correctly identified genuine messages. We interpret this as an increase in caution. In addition, we find suggestive evidence that genuine messages which contain scam-like features are more likely to be misclassified, highlighting the importance of a careful design of official communication.

Shifting Punishment onto Minorities: Experimental Evidence of Scapegoating   (NEW!)
Economic Journal, 2023, 133(652), 1626-1640. with Michal Bauer, Julie Chytilová, Gérard Roland, and Tomáš Želinský
This paper provides experimental evidence showing that members of a majority group systematically shift punishment on innocent members of an ethnic minority. We develop a new incentivized task, the Punishing the Scapegoat Game, to measure how injustice affecting a member of one’s own group shapes punishment of an unrelated party (“a scapegoat”). We study interactions between the majority group and the Roma minority in Slovakia. By experimentally manipulating the ethnic identity of the scapegoats, we show that the punishment “passed” on innocent individuals more than doubles when they are from the minority, as compared to when they are from the dominant group. These results illuminate a mechanism how individualized tensions can be transformed into a group conflict, dragging minorities into conflicts that are completely unrelated to their behavior.

Communicating doctors’ consensus persistently increases COVID-19 vaccinations
Nature, 2022, 606, 542–549.
with Vojtěch Bartoš, Michal Bauer, and Julie Chytilová
The reluctance of people to get vaccinated represents a fundamental challenge to containing the spread of deadly infectious diseases1,2, including COVID-19. Identifying misperceptions that can fuel vaccine hesitancy and creating effective communication strategies to overcome them are a global public health priority3,4,5. Medical doctors are a trusted source of advice about vaccinations6, but media reports may create an inaccurate impression that vaccine controversy is prevalent among doctors, even when a broad consensus exists7,8. Here we show that public misperceptions about the views of doctors on the COVID-19 vaccines are widespread, and correcting them increases vaccine uptake. We implement a survey among 9,650 doctors in the Czech Republic and find that 90% of doctors trust the vaccines. Next, we show that 90% of respondents in a nationally representative sample (n = 2,101) underestimate doctors’ trust; the most common belief is that only 50% of doctors trust the vaccines. Finally, we integrate randomized provision of information about the true views held by doctors into a longitudinal data collection that regularly monitors vaccination status over 9 months. The treatment recalibrates beliefs and leads to a persistent increase in vaccine uptake. The approach demonstrated in this paper shows how the engagement of professional medical associations, with their unparalleled capacity to elicit individual views of doctors on a large scale, can help to create a cheap, scalable intervention that has lasting positive impacts on health behaviour.

Foretelling What Makes People Pay: Predicting the Results of Field Experiments on TV Fee Enforcement 
Journal of Behavioral and Experimental Economics, 2022, Volume 100, 101902.
with Kateřina Chadimová and Lubomír Cingl
Forecasts of research results can aid evaluation of their novelty and credibility by indicating whether the results should be regarded as surprising, and by helping to mitigate publication bias against null results. Further, surprising differences between predictions and field results might help identify candidates for replication studies, an important task in ensuring research transparency. We run a laboratory experiment in which non-experts forecast the results of two large field experiments on TV license fee collection, to evaluate the degree to which they can successfully predict these results. In our setting, forecasters successfully identified the most effective treatments applying a deterrence motive but struggled to forecast the results of “soft” behavioral treatments compared to the baseline. However, they were mostly correct when forecasting same effectiveness of the “soft” treatments compared to each other. Our results suggest that, despite the artificiality of the laboratory environment, forecasts generated there can improve the informativeness and interpretation of research results to some extent.

 Covid-19 and Hostility against Foreigners
European Economic Review, 2021, 137, 103818.
with Vojtěch Bartoš, Michal Bauer, and Julie Chytilová
Harmful behavior against out-group members often rises during periods of economic hardship and health pandemics. Here, we test the widespread concern that the Covid-19 crisis may fuel hostility against people from other nations. Using a controlled money-burning task, we elicited hostile behavior among a nationally representative sample (n=2,186) in the Czech Republic during the first wave of the pandemic. We provide evidence that exogenously elevating salience of the Covid-19 crisis increases hostility against foreigners from the EU, USA and Asia. This behavioral response is similar across various demographic sub-groups. Further, we do not find support for the optimistic view that the Covid-19 crisis may create stronger social bonds within a country. The results underscore the importance of not inflaming anti-foreigner sentiments and suggest the need to monitor impacts of the crisis on behavior in the social domain.

How Stress Affects Performance and Competitiveness across Gender
Management Science, 2020, 66(8): 3295-3310.
with Lubomir Cingl and Ian Levely
Because many key career events, such as examinations and interviews, involve competition and stress, gender differences in response to these factors could help to explain the labor market gender gap. In a laboratory experiment, we manipulate psychosocial stress using the Trier Social Stress Test and confirm that this is effective by measuring salivary cortisol level and heart rate. Subjects perform in a real-effort task under both tournament and piece-rate incentives, and we elicit willingness to compete. We find that women under heightened stress perform worse than women in the control group when compensated with tournament incentives, whereas there is no treatment difference under piece-rate incentives. For men, stress does not affect output under competition or under piece rate. The gender gap in willingness to compete is not affected by stress, but stress decreases competitiveness overall, which is related to performance for women. Our results could explain gender differences in performance under competition, with implications for hiring practices and incentive structures in firms.

Social Contagion of Ethnic Hostility.
with Michal Bauer, Julie Chytilová, and Tomáš Želinský
Interethnic conflicts often escalate rapidly. Why does the behavior of masses easily change from cooperation to aggression? This paper provides an experimental test of whether ethnic hostility is contagious. Using incentivized tasks, we measured willingness to sacrifice one’s own resources to harm others among adolescents from a region with a history of animosities toward the Roma people, the largest ethnic minority in Europe. To identify the influence of peers, subjects made choices after observing either destructive or peaceful behavior of peers in the same task. We found that susceptibility to follow destructive behavior more than doubled when harm was targeted against Roma rather than against coethnics. When peers were peaceful, subjects did not discriminate. We observed very similar patterns in a norms-elicitation experiment: destructive behavior toward Roma was not generally rated as more socially appropriate than when directed at coethnics, but the ratings were more sensitive to social contexts. The findings may illuminate why ethnic hostilities can spread quickly, even in societies with few visible signs of interethnic hatred.

Risk Preferences under Acute Stress
Experimental Economics 2017,  20(1): 209-236.

with Lubomír Cingl
Many important decisions are made under stress and they often involve risky alternatives. There has been ample evidence that stress influences decision making in cognitive as well as in affective domains, but still very little is known about whether individual attitudes to risk change with exposure to acute stress. To directly evaluate the causal effect of stress on risk attitudes, we adopt an experimental approach in which we randomly expose participants to a psychosocial stressor in the form of a standard laboratory stress-induction procedure: the Trier Social Stress Test for Groups. Risk preferences are elicited using an incentive compatible task, which has been previously shown to predict risk-oriented behavior out of the laboratory. Using three different measures (salivary cortisol levels, heart rate and multidimensional mood questionnaire scores), we show that stress was successfully induced on the treatment group. Our main result is that acute psychosocial stress significantly increases risk aversion. The effect is mainly driven by males; men in our control group are less risk-averse than women, which is a standard result in the literature, but this difference almost disappears when under psychosocial stress.

Working papers

Carrots, Sticks, or Simplicity: Field Evidence on What Makes People Pay TV Fees
Reject&resubmit at the Economic Journal

with Kateřina Chadimová, Lubomír Cingl, and Miroslav Zajíček
We provide evidence on both innovative as well as known behavioral strategies aimed at improving tax compliance, using a unified environment of two large correspondence experiments (N=82,599 and N=51,142) with potential TV-fees evaders in the Czech Republic. We (i) simplify the original letter and add a QR code for easier registration; use two innovative text strategies aimed at (ii) the elicitation of preference for fee designation, and (iii) the explanation of fee purpose. We also employ strategies known in the literature but providing mixed results: highlighting (iv) legal consequences of non-compliance, (v) value of services for the fee, and (vi) social norms. Apart from the text treatments, we modify the envelopes by placing there (vii) a picture of a cartoon character (supported by a sticker inside), or (viii) a red inscription “Important”, with the aim to stimulate recipients’ reciprocity and attention. Our results show that the text simplification and highlighting legal consequences substantially improve effectiveness of the letter, which we self-replicate on a new sample two years later, while the remaining treatments do not improve over the baseline. The QR code brings only a modest improvement.

Study Abroad Experience and Attitudes Towards Other Nationalities
CERGE-EI Working Paper Series, No. 556, 2015.

Every year, millions of people move to a foreign country for school or work. This research provides evidence of how such international experience shifts preferences and stereotypes towards other nationalities. I use the largest study abroad program in the world—the Erasmus program—as a source of variation in international experience. Students about to participate in the Erasmus program are taken as a control group for students who have just returned. Individuals make decisions in a Trust Game and in a Triple Dictator Game to decompose changes to statistical discrimination from changes to taste-based discrimination. Results show that while students prior to an Erasmus stay do not differentiate between partners from Northern and Southern Europe in the Trust Game, students with Erasmus experience start to exhibit lower trust towards partners from the South. Behavior towards other nationalities in the Triple Dictator Game is not affected by Erasmus. Overall, the results suggest that participants learn about cross-country variation in cooperative behavior while abroad and therefore statistical discrimination becomes more relevant with increased international experience.

Selected work in progress

Youngism: Experimental Evidence (with V. Bartoš, M. Bauer, and J. Chytilová)

Life during the Pandemic (with Vojtěch Bartoš, Michal Bauer, and Julie Chytilová) – some aggregate data are published at (in Czech). Cite data as: Daniel Prokop, Vojtěch Bartoš, Michal Bauer, Jana Cahlíková, Julie Chytilová, Michaela Kudrnáčová, Lucie Marková, Eliška Dvořáková, Tomáš Hovorka (2021): Life during the pandemic: Longitudinal data set from the Czech Republic. URL:

Other writings

The impacts of the COVID-19 pandemic on mental health (A study for the Institute for Democracy and Economic Analysis IDEA; in Czech, with Vojtěch Bartoš, Michal Bauer, and Julie Chytilová; in Czech with an English summary; 2020)