Amnon Rapoport made seminal contributions to research on investment decision-making and individual decision-making under risk. To build on his seminal work, this paper explores the impact of social influence on risk-taking. First, to build predictions for experimental testing, we modify a standard expected utility model by introducing a social norm variable. Using a standard 10-decision paired lottery choice task, we report the results from three experiments with different manipulations to test whether social influence information affects subjects’ own lottery choices. In Experiment 1, we find that participants are more likely to switch to choosing the risky option earlier if they are told that a large majority (>75%) of a large group (N = 100) of others have also chosen the risky option in the past. In Experiment 2, we find there is no effect if the social influence prompt is framed as a small group (N = 10) or the choice of one (N = 1) successful lottery participant, but there is an effect when participants are provided information about the consistently risky choices of one (N = 1) person in the past. In Experiment 3, using an in-person subject pool, we find some mixed effects on risk-taking when the social information is framed as a small group (N = 10) of peers (other students). Altogether, this paper demonstrates that social influence can impact risk-taking in line with a socially normed expected utility model.

This introduction presents the two-part Special Issue of honoring the life and work of Amnon Rapoport (1936–2022), a pioneering scholar whose six decades of research shaped experimental studies of interactive decision making. Rapoport’s hallmark was the interplay between formal game-theoretic modeling and rigorous laboratory testing, advancing understanding in coalition formation, social dilemmas, market entry, traffic networks, decision timing, resource dilemmas, behavioral operations, and methodological innovation. The 27 articles collected across the volumes revisit and extend these themes, offering fresh insights into how rationality assumptions succeed and fail in predicting human behavior. Together, the contributions reflect both continuity with Rapoport’s intellectual credo—“model first, test second, refine third”—and renewal through new methods and applications. Beyond scholarship, the issue pays tribute to Rapoport’s extraordinary role as a mentor and his enduring influence on the evolution of behavioral and experimental economics

Many societies allocate wealth and status through competitions. These competitions may be seen as unfair if the playing field is uneven or if the competitors are of unequal strength. We run two experiments to document the extent to which people are willing to compete against others in situations with varying fairness concerns. In a between-subject experiment, we show that people’s willingness to compete is largely unaffected by the impact their choice has on the payoff of an opponent, no matter whether the opponent had a choice about whether to compete or not. In a within-subject experiment, we show that most people are willing to compete against opponents who have been exogenously disadvantaged or are known to be weaker. People who choose competition against weak or disadvantaged opponents are also more willing to give themselves an advantage by sabotaging the performance of their opponent.

An abundance of statistics has shown gender disparity in hiring decisions. This paper shows that a previously unexplored factor, the decision-making process utilized by a hiring committee, plays a crucial role. Using a laboratory experiment, we find that gender disparity is eliminated when hiring decisions are made unanimously by a group. By comparison, we find that gender disparity is largest when decisions are made by a leader who volunteers. We do not find evidence of heterogeneity by gender as the results persist regardless of the number of women in the group or the leader’s gender. The experimental design allows us to rule out several possible mechanisms including differences in leadership characteristics and communication styles.

We introduce a novel scenario that embeds the Downs-Thomson paradox in the context of departure-time choice during the morning commute. Commuters, departing from a common origin and traveling to a common destination, must choose between a congestible mode (car, road) and a non-congestible mode (train, railway). Those choosing the road must also select their departure times independently and anonymously. This decision involves a trade-off between the cost of queuing at the bottleneck and the cost of schedule delay (i.e., deviation from the desired arrival time). We numerically derive a symmetric mixed-strategy equilibrium that characterizes both mode and departure-time choices. We then examine how improvements to either the road or the railway affect mean travel costs. Our laboratory experiment shows that, consistent with the paradox, improving the railway lowers mean travel cost; however, contrary to the paradox, improving the road also reduces mean travel cost. These findings suggest that the Downs-Thomson paradox may fail to emerge fully when commuters must coordinate multiple strategic dimensions under intertemporal congestion externalities.

Using data from a large-scale behavioral experiment in Beijing, we investigate how social efficiency orientation may relate to rice culture proxied by the rice farming ratio in the subject’s birth province. We find that the observed behavior in several behavioral games that enhances social efficiency is positively associated with the rice farming ratio. This is corroborated by a further analysis of data related to giving help from the China Family Panel Studies. The overall finding supports our hypothesis that rice culture fosters the individual’s intrinsic preference toward greater social efficiency.

Our study contributes to the literature on choice shifts in group decision-making by analyzing how the level of risk-taking within a group is influenced by its gender composition. In particular, we investigate experimentally whether group composition affects how preferences ‘shift’ when comparing individual and group choices. Consistent with hypotheses derived from previous literature, we show that male-dominated groups shift toward riskier decisions in a way that is not explained by any simple preference aggregation mechanism. We discuss potential channels for the observed pattern of choice shifts.

We introduce the “Fork Game,” a graphical interface designed to elicit higher-order risk preferences. In this game, participants connect forked pipes to create a final structure. A ball is then dropped into the top opening of this structure and follows a downward path, randomly turning left or right at each forked joint. This construction is effectively isomorphic to the apportionment of binary-outcome lotteries, allowing participants to construct complex gambles. Furthermore, the game is easily comprehensible, highly modular, and provides a flexible means of assessing risk aversion, prudence, temperance, and even higher-order risk preferences.

We present and test a model of reciprocity in which people are more likely to repay good treatment to the extent they judge it as motivated by true caring rather than tactical self-interest. The model’s key contributions stem from how it handles ambiguously motivated behavior. It allows people to maintain divergent hypotheses: They can view behavior as driven by caring, self-interest, or a mix thereof. In contrast, previous analyses resolve rather than maintain ambiguity. They treat caring and self-interest as mutually exclusive hypotheses, and require that people commit to one and dismiss the other. By more realistically handling ambiguity, our model yields three benefits. First, it accommodates intuitive patterns of play that existing analyses do not and which we experimentally corroborate. These patterns reflect intermediate inclinations to reciprocate ambiguously motivated positive behavior. Second, it challenges conventional interpretations of long-studied phenomena, including unraveling in finitely iterated prisoners’ dilemmas, substantial offers in ultimatum games, and gift exchange. Third, it highlights how diversity in perceptions – the same action can appear generous to one person and miserly to another – is empirically consequential. Under conventional interpretations and without accounting for diverse perceptions, the aforementioned phenomena have been viewed as inconsistent with a taste for repaying good treatment. Our model shows that they are entirely consistent with a nuanced form of this taste: a desire to repay good treatment that seems to largely reflect genuine caring.

We conduct an economic experiment to examine the causal impact of social ties on the preference for competition. Participants decide whether to engage in a competition or not. Across four treatments, potential competitors vary based on their relationship with the decision-maker: whether they had a conversation with the decision-maker prior to the competition, whether they are expected to chat after the competition, or both, or neither. We find that the process of chatting increases social closeness. This increase in social closeness tends to reduce the preference for competition when participants are expected to meet again after the competition. However, it does not change the likelihood of opting for competition if there is no prospect of further interaction. Through this experiment, we thus uncover previously unknown implications of managerial practices, such as team-building exercises and remote work options, that influence the formation of social ties.

In the presence of a default option, the optimal search rule for an agent with a reference-dependent utility and a search cost predicts: (i) the default increases the reservation utility due to the reference effect, leading to a better choice, and (ii) those with higher reservation utility will self-select into search and are more likely to find a superior option. Our experiments document the presence of both effects. Those who reject the default are likely to find higher-ranked options in their active search, supporting the self-selection effect. Even when the self-selection channel is shut down, the reference effect remains.

We report a lab experiment to study subjects’ preferences over their ordinal rank in an earnings distribution. Following an assignment of unequal earnings, subjects can select a monetary transfer from exactly one individual to another, not including themselves. This can potentially change their own position in the distribution, as well as influence overall inequality. The experiment varies whether the initial earnings assignment is random or is affected by preliminary competition. It also varies the reference group from a complete to a partial network. A majority of observed transfers reduce inequality by moving earnings from those with the highest rank to the lowest rank in the distribution. Rank-improving transfers are substantially more common for preliminary competition losers than winners. Transfers to individuals outside of the reference group are not uncommon, and they usually target as the source the individuals high in the income distribution. While generally weak overall, own rank preferences appear to be more common among men than women.

In this paper, we present a flexible approach to estimating parametric cumulative Prospect Theory using Hierarchical Bayesian methods. Bayesian methods allow us to include prior knowledge in estimation and heterogeneity in individual responses. The model employs a generalised parametric specification of the value function allowing each individual to be risk-seeking in low-stakes mixed prospects. In addition, it includes parameters accounting for varying levels of model noise across domains (gain, loss, and mixed) and several aspects of lottery design that can influence respondent behaviour. Our results indicate that enhancing value function flexibility leads to improved model performance. Our analysis reveals that choices within the gain domain tend to be more predictable. This implies that respondents find tasks in the gain domain cognitively less challenging in comparison to making choices within the loss and mixed domains.

Efficient coordination is a major source of efficiency gains. We study in an experimental coordination game with 727 children and teenagers, aged 9 to 18 years, the strategies played in pre-adulthood. In our one-shot, experimental coordination game, we vary the incentives for reaching the more efficient equilibrium and the number of subjects within a group. Looking at strategy choices dependent on age, we do not find robust age effects in the aggregate. Yet, we see that smaller group sizes and larger incentives increase the likelihood of choosing the efficient strategy. The larger strategic uncertainty in larger groups is obviously harmful for overall efficiency. Regarding incentives, we find that increasing the profits in the efficient equilibrium seems to work better than providing a cushion in case of miscoordination. Beliefs play an important role as well, as subjects are more likely to play the efficient strategy when they expect others to do so as well. Our results are robust to controlling for individual risk-, time-, and social preferences.

Previous studies have shown that an oath can reduce lying in individual settings. Can it reduce lying in groups, a context where lying is more prevalent? Results from a lab experiment reveal that the impact depends on the incentive structures and procedures. A mandatory oath reduces lying when group members’ payoffs are independent, but only has a marginal effect when payoffs are dependent. Voluntary oath-taking enhances the effectiveness under both incentive structures by fostering intrinsic motivation to keep promises. The findings highlight the importance of peer effects and oath-taking procedures on the effectiveness of an oath in group settings.

We explore strategic betting in competitive environments with multiple participants and potential winners. We examine two scenarios: an ‘inclusive’ low-competition scenario with many winners and an ‘exclusive’ high-competition scenario with few winners. Using a simple model, we illustrate the strategic insights in these scenarios and present experimental results that align with our predictions. In the experiment, participants made repeated bets with feedback on past results and their payoffs. In the inclusive scenario, all but the worst guessers were rewarded, while in the exclusive scenario, only the top guessers received rewards. Our findings show that in the inclusive scenario, participants exhibit herding behavior by coordinating their bets, while in the exclusive scenario, they diversify their bets across multiple options. The main general insight of our findings is that in moderate competitions, one tends to join the majority to avoid standing out in case of failure, whereas in intense competitions, one tends to differentiate oneself from one’s peers to ensure that success stands out. This insight is relevant for a broad domain of strategic interactions.

This paper investigates the collusive and competitive effects of algorithmic price recommendations on market outcomes. These recommendations are often non-binding and common in many markets. We develop a theoretical framework and derive two algorithms that recommend collusive pricing strategies. Utilizing a laboratory experiment, we find that sellers condition their prices on the recommendation of the algorithms. The algorithm with a soft punishment strategy lowers market prices and has a pro-competitive effect. The algorithm that recommends a subgame perfect equilibrium strategy increases the range of market outcomes, including more collusive ones.

We propose a two-sided market entry game and present experiments studying coordination behavior in the game. The two-sided market in the game is operated by an intermediary monopoly platform, serving two sides (i.e., customers and service providers) and featuring asymmetric agents, cross-side network effects, and endogenous market capacity. The game has multiple pure-strategy Nash equilibria if at least one side has a high willingness to enter the market and the other side’s willingness is not very low. We conduct a laboratory experiment involving three treatments corresponding to different combinations of willingness to enter the market among customers and service providers. The experimental results indicate that willingness to enter the market and cross-side network effects significantly influence coordination behavior in two-sided markets. When the multiple pure-strategy Nash equilibria are Pareto ranked on both sides, customers and service providers can coordinate their behavior to the payoff-dominant equilibrium via tacit coordination under strategic uncertainty. However, when the multiple pure-strategy Nash equilibria are Pareto ranked on one side but Pareto equivalent on the other side, coordination failure and disequilibrium occurred, and the equilibria cannot predict the aggregate behavior well. Our experimental results indicate that a thriving two-sided market should coordinate both sides on board.

Determining an individual’s strategic reasoning capability based solely on choice data is a complex task. This complexity arises because sophisticated players might have non-equilibrium beliefs about others, leading to non-equilibrium actions. In our study, we pair human participants with computer players known to be fully rational. This use of robot players allows us to disentangle limited reasoning capacity from belief formation and social biases. Our results show that, when paired with robots, subjects consistently demonstrate higher levels of rationality, compared to when paired with human players. Furthermore, players’ rationality levels are relatively stable across games when paired with robot players, even though those with intermediate rationality levels exhibit inconsistency across games. Leveraging our experimental design, we identify and document potential causes of this inconsistency.

Volunteering is a widespread allocation mechanism in the workplace. It emerges naturally in software development or the generation of online knowledge platforms. Using a field experiment with more than 2,000 workers, we study the effect of team size on volunteering in an online labor market. In contrast to our theoretical predictions and previous research, we find no effect of team size on volunteering, although workers react to free-riding incentives, and volunteering is perceived as costly. Eliciting workers’ beliefs about their co-workers’ volunteering reveals conditional volunteering as the primary driver of our results: Workers tend to volunteer more when they believe that others are volunteering, even when doing so is highly inefficient. Using additional experiments, we identify the importance of the task itself as an essential mitigating factor for those results.