This experiment investigates decisions made by prospective economists and physicians in an allocation problem which can be framed either medically or neutrally. The potential recipients differ with respect to their minimum needs as well as to how much they benefit from a treatment. We classify the allocators as either 'selfish', 'Rawlsian', or 'maximizing the number of recipients'. Economists tend to maximize their own payoff, whereas the physicians' choices are more in line with maximizing the number of recipients and with Rawlsianism. Regarding the framing, we observe that professional norms surface more clearly in familiar settings. Finally, we scrutinize how the probability of being served and the allocated quantity depend on a recipient's characteristics as well as on the allocator type.JEL Classification: A13, I19, C91, C72

In an influential paper, Kosfeld et al. (2005) showed that intranasal administration of oxytocin (OT) increases the transfers made by investors in the trust game-suggesting that OT increases trust in strangers. Subsequent studies investigating the role of OT in the trust game found inconclusive effects on the trusting behaviour of investors but these studies deviated from the Kosfeld et al. study in an important way-they did not implement minimal social contact (MSC) between the investors and the trustees in the trust game. Here, we performed a large double-blind and placebo-controlled replication study of the effects of OT on trusting behaviour that yields a power of more than 95% and implements an MSC condition as well as a no-social-contact (NoC) condition. We find no effect of OT on trusting behaviour in the MSC condition. Exploratory post hoc analyses suggest that OT may increase trust in individuals with a low disposition to trust in the NoC condition, but this finding requires confirmation in future research.

The history of humankind is an epic of cooperation, which is ubiquitous across societies and increasing in scale. Much human cooperation occurs where it is risky to cooperate for mutual benefit because successful cooperation depends on a sufficient level of cooperation by others. Here we show that arginine vasopressin (AVP), a neuropeptide that mediates complex mammalian social behaviors such as pair bonding, social recognition and aggression causally increases humans' willingness to engage in risky, mutually beneficial cooperation. In two double-blind experiments, male participants received either AVP or placebo intranasally and made decisions with financial consequences in the "Stag hunt" cooperation game. AVP increases humans' willingness to cooperate. That increase is not due to an increase in the general willingness to bear risks or to altruistically help others. Using functional brain imaging, we show that, when subjects make the risky Stag choice, AVP down-regulates the BOLD signal in the left dorsolateral prefrontal cortex (dlPFC), a risk-integration region, and increases the left dlPFC functional connectivity with the ventral pallidum, an AVP receptor-rich region previously associated with AVP-mediated social reward processing in mammals. These findings show a previously unidentified causal role for AVP in social approach behavior in humans, as established by animal research.vasopressin | intranasal administration | cooperation | fMRI | neuroeconomics

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Structured peer-to-peer systems allow to administer large volumes of data. Several peers collaborate to generate a query result. Analyses of unstructured peer-to-peer systems, namely of those for file-sharing, show that peers tend to shirk collaboration. We anticipate similar behavior in structured peer-to-peer systems.Recently, protocols to counter uncooperative behavior in such systems have been proposed. This article examines the behavior of peers under such protocols, using game theory. A first result of this paper is a set of hypotheses, e.g.: Peers answer queries if more than a certain percentage of their queries is answered. In many situations, free-riding does not lead to a break-down of the system. Trust, reciprocity and reputation building via a feedback mechanism are behavioral motives that increase cooperation. As a second step, we have conducted economic experiments with human participants to validate our predictions. Such experiments are important because we do not need to make any assumptions regarding the behavior of peers. It turns out that the predictions remain valid in these experiments.

Divide the decision-maker's future into: (i) a pre-outcome period (lasting from the decision until the outcome of that decision is known), and (ii) a sequel post-outcome period (beginning when the outcome becomes known). Anticipated emotions in both periods may influence the decision, in particular, with regard to an outcome that matters to the person, the enjoyable tension from not yet knowing what this outcome will be. In the experiments presented, lottery choice can be explained by this attraction to chance, and cannot be explained by either convex von Neumann-Morgenstern utility, or by rank-dependent risk-loving weights: attraction to chance is a separate motivator. Copyright Verein fü Socialpolitik and Blackwell Publishers Ltd 2000.

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