Social preferences trump emotions in human responses to unfair offers.

People commonly reject unfair offers even if this leaves them worse off. Some explain this as a rational response based on social preferences. Others argue that emotions override self-interest in the determination of rejection behavior. We conducted an experiment in which we measured responders' biophysical reactions (EEG and EMG) to fair and unfair offers. We measured biophysical trait anger using resting-state EEG (frontal alpha-asymmetry), state anger using facial expressions, offer expectancy processing using event-related EEG (medial-frontal negativity; MFN) and self-reported emotions. We systematically varied whether rejections led proposers to lose their share (Ultimatum Game; UG) or not (Impunity Game; IG). Results favor preference-based accounts: Impunity minimizes rejection despite increasing subjectively reported anger. Unfair offers evoke frowning responses, but frowning does not predict rejection. Prosocial responders reject unfair UG offers more often after unmet fairness expectations. These results suggest that responders do not reject unfairness out of anger. Rather, people seem motivated to reject unfair offers when they violate their behavioral code but only when rejection has payoff consequences for the proposer, allowing them to reciprocate and restore equity. Thus, social preferences trump emotions when responding to unfair offers.

The competitive advantage of sanctioning institutions revisited: A multilab replication.

Is peer sanctioning a sustainable solution to the problem of human cooperation? We conducted an exact multilab replication (N = 1,008; 7 labs × 12 groups × 12 participants) of an experiment by Gürerk, Irlenbusch, and Rockenbach published in Science in 2006 (Gürerk Ö, Irlenbusch B, Rockenbach B. The competitive advantage of sanctioning institutions. 2006. Science. 312(5770):108-111). In GIR2006 (N = 84; 1 lab × 7 groups × 12 participants), groups that allowed members to reward cooperators and punish defectors were found to outgrow and outperform groups without a peer-sanctioning institution. We find GIR2006 replicated in accordance with all preregistered replication criteria in five of the seven labs we sampled. There, the majority of participants joined groups with a sanctioning institution, and participants cooperated and profited more on average than in groups without a sanctioning institution. In the two other labs, results were weaker but still favored sanctioning institutions. These findings establish the competitive advantage of sanctioning institutions as a robust phenomenon within the European context.

Network segregation and the propagation of misinformation.

How does the ideological segregation of online networks impact the spread of misinformation? Past studies have found that homophily generally increases diffusion, suggesting that partisan news, whether true or false, will spread farther in ideologically segregated networks. We argue that network segregation disproportionately aids messages that are otherwise too implausible to diffuse, thus favoring false over true news. To test this argument, we seeded true and false informational messages in experimental networks in which subjects were either ideologically integrated or segregated, yielding 512 controlled propagation histories in 16 independent information systems. Experimental results reveal that the fraction of false information circulating was systematically greater in ideologically segregated networks. Agent-based models show robustness of this finding across different network topologies and sizes. We conclude that partisan sorting undermines the veracity of information circulating on the Internet by increasing exposure to content that would otherwise not manage to diffuse.

Realtime user ratings as a strategy for combatting misinformation: an experimental study.

Because fact-checking takes time, verdicts are usually reached after a message has gone viral and interventions can have only limited effect. A new approach recently proposed in scholarship and piloted on online platforms is to harness the wisdom of the crowd by enabling recipients of an online message to attach veracity assessments to it. The intention is to allow poor initial crowd reception to temper belief in and further spread of misinformation. We study this approach by letting 4000 subjects in 80 experimental bipartisan communities sequentially rate the veracity of informational messages. We find that in well-mixed communities, the public display of earlier veracity ratings indeed enhances the correct classification of true and false messages by subsequent users. However, crowd intelligence backfires when false information is sequentially rated in ideologically segregated communities. This happens because early raters' ideological bias, which is aligned with a message, influences later raters' assessments away from the truth. These results suggest that network segregation poses an important problem for community misinformation detection systems that must be accounted for in the design of such systems.

Prioritizing high-contact occupations raises effectiveness of vaccination campaigns.

A twenty-year-old idea from network science is that vaccination campaigns would be more effective if high-contact individuals were preferentially targeted. Implementation is impeded by the ethical and practical problem of differentiating vaccine access based on a personal characteristic that is hard-to-measure and private. Here, we propose the use of occupational category as a proxy for connectedness in a contact network. Using survey data on occupation-specific contact frequencies, we calibrate a model of disease propagation in populations undergoing varying vaccination campaigns. We find that vaccination campaigns that prioritize high-contact occupational groups achieve similar infection levels with half the number of vaccines, while also reducing and delaying peaks. The paper thus identifies a concrete, operational strategy for dramatically improving vaccination efficiency in ongoing pandemics.

COVID-19 vulnerability and perceived norm violations predict loss of social trust: A pre-post study.

While pandemic containment measures benefit public health, they may jeopardize the social structure of society. We hypothesize that lockdowns and prolonged social distancing measures hinder social support and invite norm violations, eroding social trust. We conducted a pre-registered pre-post study on a representative sample of the Dutch population (n = 2377; participation rate = 88.8%), measuring social trust reported by the same individuals before and after the first wave of the COVID-19 pandemic. Results show that social trust in the Netherlands suddenly dropped from its historically stable level, reaching one of its lowest points on record. The decline was stronger among residents belonging to official high-risk categories, especially if they perceived themselves as likely to become infected. Individuals who more strongly agreed with self-isolation norms or did not perceive a widespread compliance or agreement with such norms also reported a greater loss of trust.

"Stay nearby or get checked": A Covid-19 control strategy.

This paper repurposes the classic insight from network theory that long-distance connections drive disease propagation into a strategy for controlling a second wave of Covid-19. We simulate a scenario in which a lockdown is first imposed on a population and then partly lifted while long-range transmission is kept at a minimum. Simulated spreading patterns resemble contemporary distributions of Covid- 19 across EU member states, German and Italian regions, and through New York City, providing some model validation. Results suggest that our proposed strategy may significantly reduce peak infection. We also find that post-lockdown flare-ups remain local longer, aiding geographical containment. These results suggest a tailored policy in which individuals who frequently travel to places where they interact with many people are offered greater protection, tracked more closely, and are regularly tested. This policy can be communicated to the general public as a simple and reasonable principle: Stay nearby or get checked.

Reputations in mixed-role markets: A theory and an experimental test.

The traditional understanding of reputation systems is that they secure trust between strangers by publicly calling out cheaters. In modern, online markets, it is increasingly common for providers of a good to also act as consumers, and vice versa. We argue that in such mixed-role markets, reputation systems serve a second important function: They allow providers who lend out their possessions (such as their house, car or tools) to earn reputational credits that can be spent on future borrowing, especially when lending lacks monetary compensation. In an experiment that introduces a new game, "the Lending Game", we show that, consistent with our argument, information on past lending leads subjects to lend to those who have themselves lent before, increasing overall lending. However, when lending is financially compensated, this mechanism of reciprocal lending ceases to operate.

All-sense-all networks are suboptimal for sensorimotor synchronization.

In human groups that seek to synchronize to a common steady beat, every member can typically perceive every other member. We question whether this naturally occurring all-sense-all condition is optimal for temporal coordination. We consider alternative configurations represented by directed graphs, in which individuals can only hear or see a subset of others. We identify a trade-off in the topology of such networks: While denser graphs provide stronger coupling, improving synchrony, density increases sensitivity to early taps, which produces rushing. Results from an experimental study with music conservatory students show that networks that combine short path length with low density match all-sense-all networks in synchrony while yielding a steadier beat. These findings suggest that professional teams in arts, sports, industry, and the military may improve temporal coordination by employing technology that strategically configures who can track whom.

The Matthew effect in science funding.

A classic thesis is that scientific achievement exhibits a "Matthew effect": Scientists who have previously been successful are more likely to succeed again, producing increasing distinction. We investigate to what extent the Matthew effect drives the allocation of research funds. To this end, we assembled a dataset containing all review scores and funding decisions of grant proposals submitted by recent PhDs in a €2 billion granting program. Analyses of review scores reveal that early funding success introduces a growing rift, with winners just above the funding threshold accumulating more than twice as much research funding (€180,000) during the following eight years as nonwinners just below it. We find no evidence that winners' improved funding chances in subsequent competitions are due to achievements enabled by the preceding grant, which suggests that early funding itself is an asset for acquiring later funding. Surprisingly, however, the emergent funding gap is partly created by applicants, who, after failing to win one grant, apply for another grant less often.

Racial and gender differences in missing children's recovery chances.

We inquire whether there are race and gender differences in the recovery of missing children. We argue that race and gender differences may arise due to differential media attention, socio-economic background and police resources. Datasets used in previous research lack the representativeness and longitudinal character necessary for probing victim demographic effects on recovery success. Here we use official New York State Division of Criminal Justice Services records of all children reported missing in the period 2007-2010 containing exact dates of disappearance and recovery. In event-history analysis of these data we find that missing boys and girls have comparable daily recovery chances. Black children, however, on average remain missing longer and are more likely to still be missing by the end of our observation period than non-black children.

Arbitrary Inequality in Reputation Systems.

Trust is an essential condition for exchange. Large societies must substitute the trust traditionally provided through kinship and sanctions in small groups to make exchange possible. The rise of internet-supported reputation systems has been celebrated for providing trust at a global scale, enabling the massive volumes of transactions between distant strangers that are characteristic of modern human societies. Here we problematize an overlooked side-effect of reputation systems: Equally trustworthy individuals may realize highly unequal exchange volumes. We report the results of a laboratory experiment that shows emergent differentiation between ex ante equivalent individuals when information on performance in past exchanges is shared. This arbitrary inequality results from cumulative advantage in the reputation-building process: Random initial distinctions grow as parties of good repute are chosen over those lacking a reputation. We conjecture that reputation systems produce artificial concentration in a wide range of markets and leave superior but untried exchange alternatives unexploited.

Choosing your network: social preferences in an online health community.

A growing number of online health communities offer individuals the opportunity to receive information, advice, and support from peers. Recent studies have demonstrated that these new online contacts can be important informational resources, and can even exert significant influence on individuals' behavior in various contexts. However little is known about how people select their health contacts in these virtual domains. This is because selection preferences in peer networks are notoriously difficult to detect. In existing networks, unobserved pressures on tie formation--such as common organizational memberships, introductions to friends of friends, or limitations on accessibility--may mistakenly be interpreted as individual preferences for interacting/not interacting with others. We address these issues by adopting a social media approach to studying network formation. We study social selection using an in vivo study within an online exercise program, in which anonymous participants have equal opportunities for initiating relationships with other program members. This design allows us to identify individuals' preferences for health contacts, and to evaluate what these preferences imply for members' access to new kinds of health information, and for the kinds of social influences to which they are exposed. The study was conducted within a goal-oriented fitness competition, in which participation was greatest among a small core of active individuals. Our results show that the active participants displayed indifference to the fitness and exercise profiles of others, disregarding information about others' fitness levels, exercise preferences, and workout experiences, instead selecting partners almost entirely on the basis of similarities on gender, age, and BMI. Interestingly, the findings suggest that rather than expanding and diversifying their sources of health information, participants' choices limited the value of their online resources by selecting contacts based on characteristics that are common sources of homophily in offline relationships. In light of our findings, we discuss design principles that may be useful for organizations and policy makers trying to improve the value of participants' social capital within online health programs.

Field experiments of success-breeds-success dynamics.

Seemingly similar individuals often experience drastically different success trajectories, with some repeatedly failing and others consistently succeeding. One explanation is preexisting variability along unobserved fitness dimensions that is revealed gradually through differential achievement. Alternatively, positive feedback operating on arbitrary initial advantages may increasingly set apart winners from losers, producing runaway inequality. To identify social feedback in human reward systems, we conducted randomized experiments by intervening in live social environments across the domains of funding, status, endorsement, and reputation. In each system we consistently found that early success bestowed upon arbitrarily selected recipients produced significant improvements in subsequent rates of success compared with the control group of nonrecipients. However, success exhibited decreasing marginal returns, with larger initial advantages failing to produce much further differentiation. These findings suggest a lesser degree of vulnerability of reward systems to incidental or fabricated advantages and a more modest role for cumulative advantage in the explanation of social inequality than previously thought.

Experimental study of informal rewards in peer production.

We test the effects of informal rewards in online peer production. Using a randomized, experimental design, we assigned editing awards or "barnstars" to a subset of the 1% most productive Wikipedia contributors. Comparison with the control group shows that receiving a barnstar increases productivity by 60% and makes contributors six times more likely to receive additional barnstars from other community members, revealing that informal rewards significantly impact individual effort.