Yixuan Shi (石艺璇)

Only one trip planner is needed for a group of friends to enjoy a pleasant trip and only one country is needed to coordinate on international talks that can be beneficial for all participating countries. We study a dynamic volunteering dilemma game in which two players choose to volunteer or wait given there have not been any volunteering actions in the past. The players can be procrastinators and the benefits of volunteering arrive later than the costs. We fully characterize the stationary Markov Strotz-Pollak equilibria. When the cost of volunteering is sufficiently small or agents’ present-bias parameters are sufficiently close, there always exists an equilibrium in which both players randomize. This equilibrium features stochastic delay, and the delay is exacerbated if one or both agents become more present-biased. However, if the agents differ significantly in their present-bias parameters, this difference may act as a ’natural coordination device’ and the unique stationary equilibrium predicts that only the less severe procrastinator volunteers, and this may result in an even quicker provision compared with the case of two exponential discounters.

In mixed electoral systems, candidates can win parliamentary seats either by securing the most votes in local districts or through party lists. Candidates’ successes of district elections often hinge on personal charisma, whereas the total number of party seats depends on the overall party vote share. We use a contest-theoretical model to examine how candidates in mixed electoral systems allocate limited campaign resources between winning district seats and increasing their party’s seat share. Under closed lists with predetermined rankings, lower-ranked candidates focus on district campaigns, while higher-ranked candidates invest in both district and party campaigns. Allocations also depend on district opponents’ list positions. Under open lists, where list-seat allocation depends on candidates’ vote shares, all candidates have incentives to contribute to party-centred campaigning.

Communication can facilitate coordination within teams, but it may also leak and reveal intentions to the opponent, as when a baseball team’s signs are stolen. We study how this tension shapes behaviour in a team contest, theoretically and in a laboratory experiment. Our theory predicts that secure communication plays a dual role: it improves internal coordination while concealing intentions from the opponent, thereby raising competition intensity, measured by effort, for all parties. The experiment provides causal evidence for these effects. When communication leaks, its concealment role disappears and teammates trade off coordination against unpredictability. We focus on the case in which coordination concerns dominate, so that in theory teammates should still communicate; yet they sometimes choose not to, producing costly coordination failures. Even so, effort remains close to its level under secure communication and well above its level without communication. Theory and experiment agree that jamming an opponent’s communication may be more effective than intercepting it.

Political parties often appear united despite containing factions with divergent preferences. We study why party defections are rare by opening the intra-party ‘black box’ through a set of game-theoretical models. In the model, the leadership sets the party’s policy platform anticipating exit threats from co-partisan rival factions. Rivals weigh policy proximity against the benefits of belonging to a larger party: smaller factions lack credible exit threat and remain loyal, while larger factions may require policy compromises. We emphasise the role of party size and show that unity can be sustained through a snowballing mechanism: once the leadership compromises and secures the loyalty of some factions, other factions become more willing to remain—even with no political concessions—because doing so places them with a larger and more powerful party. Leaders need only win part of the party to induce broader unity, implying that even internally diverse parties can remain stable.

We study how public good contributions and private transfers interact as channels of giving in unequal groups. Building on a model of altruistic preferences, we conduct a pre-registered, between-subjects experiment (n = 478) that varies income inequality and the availability of simultaneous private transfers in a repeated, two-person, non-linear public good game. Allowing transfers significantly reduces public good contributions across all tested inequality levels, as participants substitute between the two channels. Transfers occur even among equally endowed participants and from poorer to richer participants, with exploratory analysis suggesting a role for positive reciprocity. In highly unequal groups, allowing transfers improves poorer participants’ earnings without reducing those of richer participants. These findings highlight how private transfers can reduce within-group inequality without sacrificing aggregate earnings, despite crowding out public good contributions.

When teammates also compete for individual recognition, how should a leader divide a team prize? We study a team contest in which team leaders commit to fixed team-prize division before members split their effort between a team contest and an individual contest among all members. Even with symmetric agents, every pure-strategy equilibrium concentrates each team's entire prize to one member. Once a member with a small share focuses entirely on the individual battle, taking the rest of her prize share costs no team effort and strengthens the remaining contributor. Evenly matched teams give the whole prize to their stars. An outmatched team, however, may do the reverse, rewarding its non-star or diluting its contributor's prize share to steer efforts towards individual competition. The results identify individual competition as a source of endogenous specialisation within teams and show how competitive asymmetry changes both whom to reward and how concentrated the reward is.

We design an experiment to study how personal experience affects whether and how individuals intervene in others’ risky choices. Participants choose between lotteries with equal expected payoffs but different risks, with probabilities and payoffs fully known. We vary whether feedback on realised and forgone outcomes is received before or after the intervention decision. Participants can recommend an option, restrict another participant’s choices, or refrain from intervening, allowing us to examine the likelihood, direction, and intensity of intervention. We also explore possible channels, including emotional responses such as regret and rejoicing.

We study sequential public good provision when completion requires multiple costly volunteering actions and benefits deteriorate over time. In a symmetric interior equilibrium, individual volunteering rates are independent of the provision stage at a given time, but aggregate volunteering slows as contributors exit. Each contribution extends the deadline for further participation, leaving early movers with the tightest viability constraint. For a fixed provision requirement, larger volunteer pools slow aggregate volunteering and tighten early-stage participation constraints, reducing the probability of completion.