This paper introduces new experimental designs to examine how conditional cooperation and punishment behaviours respond to the full range of variation in the contributions of others. It is shown that contributions become significantly more selfish-biased as others contribute more unequally, while punishment increases both with decreasing contributions by the target player and increasing contributions by a third player. Low contributors who punish antisocially do not direct their punishment specifically toward high contributors, while their beliefs indicate that they expect to themselves be punished.

This paper reports an experimental study of the public goods game in which contributions are not submitted all at once but incrementally as coordinated in real time by a clock. Individuals press a button as soon as the clock equals their willingness to contribute. By providing information about the point at which subjects stop further contributions we find evidence for conditionally cooperative behaviour: A subject's decision to stop contributing induces an immediate reaction of the other group members.

We use instrumental variables for estimating the causal effect of beliefs on contributions in repeated public good games. The effect is about half as large as suggested by ordinary least squares. Thus, we present evidence that beliefs have a causal effect on contributions, but also that beliefs are endogenous. We compare the causal, belief-based model of contributions to alternative models based on matching the previous contributions of others and responding to one’s deviation from the average in the previous round. The causal, belief-based model performs well, indicating that beliefs have a central role in determining contributions.

We experimentally investigate whether individuals can reliably detect cooperators (the nice(r) people) in an anonymous decision environment involving “connected games.” Participants can condition their choices in an asymmetric prisoners’ dilemma and a trust game on past individual (their partner's donation share to a self-selected charity) and social (whether their partner belongs to a group with high or low average donations) information. Thus, the two measures of niceness are the individual donation share in the donation task, and the cooperativeness of one's choice in the two games. We find that high donors achieve a higher-than-average expected payoff by cooperating predominantly with other high donors. Group affiliation proved to be irrelevant.

Extensive experimental research on public good games documents that many subjects are “conditional cooperators” in that they positively correlate their contribution with (their belief about) contributions of other subjects in their peer group. The goal of our study is to shed light on what preference and decision-making patterns drive this observed regularity. We consider reciprocity, conformity, inequality aversion and residual factors, such as confusion and anchoring, as potential explanations. Effects of these drivers are separated by varying how others’ contributions are determined and the informational content of the conditioning variable across treatments. Assuming additive separability of the effects of the four drivers, we find that, of the average conditionally cooperative behavior, at least 40 percent is driven by residual factors. For the remainder, most is accounted for by inequality aversion, some by conformity and very little by reciprocity. These findings carry an important message for how to interpret conditional cooperation observed in the lab. We also discuss what these findings mean for understanding conditional cooperation in fundraising applications in the field.

We use a limited information environment to assess the role of confusion in the repeated voluntary contributions game. A comparison with play in a standard version of the game suggests, that the common claim that decision errors due to confused subjects biases estimates of cooperation upwards, is not necessarily correct. Furthermore, we find that simple learning cannot generate the kind of contribution dynamics commonly attributed to the existence of conditional cooperators. We conclude that cooperative behavior and its decay observed in public goods games is not a pure artefact of confusion and learning.

I survey the literature post Ledyard (Handbook of Experimental Economics, ed. by J. Kagel, A. Roth, Chap. 2, Princeton, Princeton University Press, 1995) on three related issues in linear public goods experiments: (1) conditional cooperation; (2) the role of costly monetary punishments in sustaining cooperation and (3) the sustenance of cooperation via means other than such punishments. Many participants in laboratory public goods experiments are “conditional cooperators” whose contributions to the public good are positively correlated with their beliefs about the average group contribution. Conditional cooperators are often able to sustain high contributions to the public good through costly monetary punishment of free-riders but also by other mechanisms such as expressions of disapproval, advice giving and assortative matching.

We replicate the strategy-method experiment by Fischbacher et al. (Econ. Lett. 71:397-404, 2001) developed to measure attitudes towards cooperation in a one-shot public goods game. We collected data from 160 students at four different universities across urban and rural Russia. Using the classification proposed by Fischbacher et al. (2001) we find that the distribution of types is very similar across the four locations. The share of conditional cooperators in our Russian subject pools is comparable to the one found by Fischbacher et al. in a Swiss subject pool. However, the distribution of the other types differs from the one found in Switzerland.

Conditional cooperation is the tendency to cooperate if and only if others do so as well. It is the most common behavior in social dilemmas. We study how the incidence of conditional cooperation in the public goods game, the most widely studied social dilemma in experimental economics, varies with group size. In a laboratory experiment, we apply the strategy method to elicit how participants’ willingness to contribute to a public good depends on other group members’ decisions. A within-subject design allows us to evaluate and compare an individual participant's contribution behavior in different-sized groups. Two main findings emerge. First, the share of players who are conditional cooperators is consistent across group sizes. Second, the strategies chosen imply that conditional cooperators hold a (correct) belief that others are more cooperative in a larger than in a smaller group.

Building cooperative communities is a crucial problem for human societies. Much research suggests that cooperation is facilitated by knowing who the cooperators and defectors are, and being able to respond accordingly. As such, anonymous games are thought to hinder cooperation. Here, we show that this conclusion is altered dramatically in the presence of conditional cooperation norms and heterogeneous beliefs about others’ behaviours. Specifically, we show that inaccurate beliefs about other players’ behaviours can foster and stabilise cooperation via social norms. To show this, we combine a community's population dynamics with the behavioural dynamics of their members. In our model, individuals can join a community based on beliefs generated by public signals regarding the level of cooperation within, and decide to cooperate or not depending on these beliefs. These signals may overstate how much cooperation there really is. We show that even if individuals eventually learn the true level of cooperation, the initially false beliefs can trigger a dynamic that sustains high levels of cooperation. We also characterise how the rates of joining, leaving and learning in the community affect the cooperation level and community size simultaneously. Our results illustrate how false beliefs and social norms can help build cooperative communities.

When do societies succeed in providing public goods? Previous research suggests that public goods contributions correlate with expectations about cooperation by others among students and other demographic subgroups. However, we lack knowledge about whether the effect of expected cooperation is causal and a general feature of populations. We fielded representative surveys (N = 8,500) in France, Germany, the United Kingdom, and the United States that included a public goods game and a novel between-subjects experiment. The experiment varied expectations about cooperation by others. We find that higher expected cooperation by others causes a significant increase in individual contributions. When classifying contribution schedules, we find that almost 50% of the population employs a conditionally cooperative strategy. These individuals are on average richer, younger, and more educated. Our results help explain the varying success of societal groups in overcoming cooperation problems and assist policymakers in the design of institutions meant to solve social dilemmas.