Simulating a real world environment is of utmost importance for achieving accurate and meaningful results in experimental economics. Offering monetary incentives is a common method of creating this environment. In general, experimenters provide the rewards at the time of experiment. In this paper, we argue that receiving the reward at the time of the experiment may lead participants to make decisions as if the money they are using were not their own. To solve this problem, we devised a “prepaid mechanism” that encourages participants to use the money as if it were their own.

Two rationales have emerged for why individuals keep their promises: (a) an emotional commitment to keep actions and words consistent, a commitment rationale and (b) avoidance of guilt due to not meeting the expectations of the promisee, an expectations rationale. We propose a new dichotomy with clearer distinctions between rationales: (1) an internal consistency rationale, which is the desire to keep actions and words consistent regardless of others’ awareness of the promise and (2) a communication rationale, which captures all aspects of promise keeping that are associated with the promisee having learned of the promise, including but not limited to promisee expectations. Using an experiment that manipulates whether promises are delivered, we find no support for the internal consistency rationale; only delivered promises are relevant. In a second experiment designed to better understand what aspect of promise delivery influences promisor behavior, we manipulate whether the promise is delivered before or after the promisee is able to take a trusting action. We find late-arriving promises are relevant though not as relevant as promises delivered before the promisee chooses whether to take the trusting action. We conclude that implicit contracting does not fully explain promise keeping, because had it done so, late-arriving promises would also be irrelevant.

In this paper we use experimental data from rural Cameroon to quantify the effect of social distance on trust and altruism. Our measure of social distance is relevant to everyday economic interactions: subjects in a Trust Game play with fellow villagers or with someone from a different village. We find that significantly more money is sent when the players are from the same village. Other factors that influence transfers at least as much as the same-village effect are gender, education and membership of rotating credit groups. To test whether Senders are motivated by altruism, they also play a Triple Dictator Game. Senders transfer significantly more money on average in the Trust Game than in the Triple Dictator Game. However, there is also a social distance effect in the Triple Dictator Game. Results from a Risk Game suggest that Trust Game transfers are uncorrelated with attitudes to risk.

We experimentally investigate to what extent people trust and honor trust when they are playing with other people’s money (OPM). We adopt the well-known trust game by Berg et al. (in Games Econ. Behav. 10:122–142, 1995), with the difference that the trustor (sender) who sends money to the trustee (receiver) does this on behalf of a third party. We find that senders who make decisions on behalf of others do not behave significantly different from senders in our baseline trust game who manage their own money. But receivers return significantly less money when senders send a third party’s money. As a result, trust is only profitable in the baseline trust game, but not in the OPM treatment. The treatment effect among the receivers is gender specific. Women return significantly less money in OPM than in baseline, while there is no such treatment effect among men. Moreover, women return significantly less than men in the OPM treatment.

We investigate the role of intentions in two-player two-stage games. For this purpose we systematically vary the set of opportunity sets the first mover can choose from and study how the second mover reacts not only to opportunities of gains but also of losses created by the choice of the first mover. We find that the possibility of gains for the second mover (generosity) and the risk of losses for the first mover (vulnerability) are important drivers for second mover behavior. On the other hand, efficiency concerns and an aversion against violating trust seem to be far less important motivations. We also find that second movers compare the actual choice of the first mover and the alternative choices that would have been available to him to allocations that involve equal material payoffs.

We use time, rather than money, as the salient component of subjects’ incentives in three workhorse experimental paradigms. The use of waiting time can be interpreted as a special type of real effort condition, in which it is particularly straightforward to achieve experimental control over incentives. The three experiments, commonly employed to study social preferences, are the dictator game, the ultimatum game and the trust game. All subjects in a session earn the same participation fee, but their choices affect the time at which they are permitted to leave the laboratory. Decisions that are associated with greater own payoff translate into the right to depart earlier. The modal proposal in both the dictator and ultimatum games is an equal split of the waiting time. In the trust game, there is substantial trust and reciprocity. Overall, social preferences are evident in time allocation decisions. We compare subjects’ decisions over time and money and find no significant differences in average decisions. The pattern of results suggests that results obtained in the laboratory with money as the medium of reward generalize to other reward media.

We analyze reciprocal behavior when moral wiggle room exists. Dana et al. (Econ Theory 33(1):67–80, 2007) show that giving in a dictator game is inconsistent with distributional preferences as the giving rate drops when situational excuses for selfish behavior are provided. Our binary trust game closely follows their design. Only a preceding stage (safe outside option vs. enter the game) is added in order to introduce reciprocity. We find significantly lower rates of selfish choices in the trust baseline in comparison to our treatments that feature moral wiggle room manipulations and a dictator baseline. It seems that reciprocal behavior is not only due to people liking to reciprocate but also because they feel obliged to do so.

We report the results of experiments conducted over the internet between two different laboratories. Each subject at one site is matched with a subject at another site in a trust game experiment. We investigate whether subjects believe they are really matched with another person, and suggest a methodology for ensuring that subjects’ beliefs are accurate. Results show that skepticism can lead to misleading results. If subjects do not believe they are matched with a real person, they trust too much: i.e., they trust the experimenter rather than their partner.

We analyze whether subjects with extensive laboratory experience and first-time participants, who voluntarily registered for the experiment, differ in their behavior. Subjects play four one-shot, two-player games: a trust game, a beauty contest, an ultimatum game, a traveler’s dilemma and, in addition, we conduct a single-player lying task and elicit risk preferences. We find few significant differences. In the trust game, experienced subjects are less trustworthy and they also trust less. Furthermore, experienced subjects submit fewer non-monotonic strategies in the risk elicitation task. We find no differences whatsoever in the other decisions. Nevertheless, the minor differences observed between experienced and inexperienced subjects may be relevant because we document a potential recruitment bias: the share of inexperienced subjects may be lower in the early recruitment waves.

Betrayal aversion has been operationalized as the evidence that subjects demand a higher risk premium to take social risks compared to natural risks. This evidence has been first shown by Bohnet and Zeckhauser (J Econ Behav 98:294–310, 2004) using an adaptation of the Becker–DeGroot–Marschak mechanism (BDM, Becker et al. Behav Sci 9:226–232, 1964). We compare their implementation of the BDM mechanism with a new version designed to facilitate subjects’ comprehension. We find that, although the two versions produce different distributions of values, the size of betrayal aversion, measured as an average treatment difference between social and natural risk settings, is not different across the two versions. We further show that our implementation is preferable to use in practice as it reduces substantially subjects’ mistakes and the likelihood of noisy valuations.

Do unbiased third-party peacekeepers build trust between groups in the aftermath of conflict? Theoretically, we point out that unbiased peacekeepers are the most effective at promoting trust. To isolate the causal effect of bias on trust, we use an iterated trust game in a laboratory setting. Groups that previously engaged in conflict are put into a setting in which they choose to trust or reciprocate any trust. Our findings suggest that biased monitors impede trust while unbiased monitors promote cooperative exchanges over time. The findings contribute to the peacekeeping literature by highlighting impartiality as an important condition under which peacekeepers build trust post-conflict.

Economic games offer a convenient approach for the study of prosocial behavior. As an advantage, they allow for straightforward implementation of different techniques to reduce socially desirable responding. We investigated the effectiveness of the most prominent of these techniques, namely providing behavior-contingent incentives and maximizing anonymity in three versions of the Trust Game: (i) a hypothetical version without monetary incentives and with a typical level of anonymity, (ii) an incentivized version with monetary incentives and the same (typical) level of anonymity, and (iii) an indirect questioning version without incentives but with a maximum level of anonymity, rendering responses inconclusive due to adding random noise via the Randomized Response Technique. Results from a large (N = 1,267) and heterogeneous sample showed comparable levels of trust for the hypothetical and incentivized versions using direct questioning. However, levels of trust decreased when maximizing the inconclusiveness of responses through indirect questioning. This implies that levels of trust might be particularly sensitive to changes in individuals’ anonymity but not necessarily to monetary incentives.

Ethnographers have recorded many instances of tokens donated as gifts to attract new partners or strengthen ties to existing ones. We study whether gifts are an effective pledge of the donor’s trustworthiness through an experiment modeled on the trust game. We vary whether the trustee can send a token before the trustor decides whether to transfer money; whether one of the tokens is rendered salient through experimental manipulations (a vote or an incentive-compatible rule of purchase for the tokens); and whether the subjects interact repeatedly or are randomly re-matched in each round. Tokens are frequently sent in all studies in which tokens are available, but repeated interaction, rather than gifts, is the leading behavioral driver in our data. In the studies with random pairs, trustors send significantly more points when the trustee has sent a token. Subjects in a fixed matching achieve comparable levels of trust and trustworthiness in the studies with and without tokens. The trustee’s decision to send a token is not predictive of the amount the trustee returns to the trustor. A token is used more sparingly whenever salient — a novel instance of endogenous value creation in the lab.

A considerable share of the literature on the evolution of human cooperation considers the question why we have not evolved to play the Nash equilibrium in prisoners’ dilemmas or public goods games. In order to understand human morality and pro-social behaviour, we suggest that it would actually be more informative to investigate why we have not evolved to play the subgame perfect Nash equilibrium in sequential games, such as the ultimatum game and the trust game. The ‘rationally irrational’ behaviour that can evolve in such games gives a much better match with actual human behaviour, including elements of morality such as honesty, responsibility and sincerity, as well as the more hostile aspects of human nature, such as anger and vengefulness. The mechanism at work here is commitment, which does not need population structure, nor does it need interactions to be repeated. We argue that this shift in focus can not only help explain why humans have evolved to know wrong from right, but also why other animals, with similar population structures and similar rates of repetition, have not evolved similar moral sentiments. The suggestion that the evolutionary function of morality is to help us commit to otherwise irrational behaviour stems from the work of Robert Frank (American Economic Review, 77(4), 593–604, 1987; Passions within reason: The strategic role of the emotions, WW Norton, 1988), which has played a surprisingly modest role in the scientific debate to date.