Anna Dreber

Winners don’t punish

A key aspect of human behaviour is cooperation. We tend to help others even if costs are involved. We are more likely to help when the costs are small and the benefits for the other person significant. Cooperation leads to a tension between what is best for the individual and what is best for the group. A group does better if everyone cooperates, but each individual is tempted to defect. Recently there has been much interest in exploring the effect of costly punishment on human cooperation. Costly punishment means paying a cost for another individual to incur a cost. It has been suggested that costly punishment promotes cooperation even in non-repeated games and without any possibility of reputation effects. But most of our interactions are repeated and reputation is always at stake. Thus, if costly punishment is important in promoting cooperation, it must do so in a repeated setting. We have performed experiments in which, in each round of a repeated game, people choose between cooperation, defection and costly punishment. In control experiments, people could only cooperate or defect. Here we show that the option of costly punishment increases the amount of cooperation but not the average payoff of the group. Furthermore, there is a strong negative correlation between total payoff and use of costly punishment. Those people who gain the highest total payoff tend not to use costly punishment: winners don’t punish. This suggests that costly punishment behaviour is maladaptive in cooperation games and might have evolved for other reasons.

Positive Interactions Promote Public Cooperation

Carrots Are Better Than Sticks The challenge of dealing with freeloaders—who benefit from a common good but refuse to pay their “fair share” of the costs—has often been met in theoretical and laboratory studies by sanctioning costly punishment, in which contributors pay a portion of their benefit so that freeloaders lose theirs. Rand et al. (p. 1272; see the news story by Pennisi and the cover) added a private interaction session after each round of the public goods game during which participants were allowed to reward or punish other members of their group. The outcome showed that reward was as effective as punishment in maintaining a cooperative mindset, and doing so via rewarding interactions allowed the entire group to prosper because less is lost to the costs of punishing. Reward is as good as punishment to promote cooperation, costs less, and increases the share out of resources up for grabs. The public goods game is the classic laboratory paradigm for studying collective action problems. Each participant chooses how much to contribute to a common pool that returns benefits to all participants equally. The ideal outcome occurs if everybody contributes the maximum amount, but the self-interested strategy is not to contribute anything. Most previous studies have found punishment to be more effective than reward for maintaining cooperation in public goods games. The typical design of these studies, however, represses future consequences for today’s actions. In an experimental setting, we compare public goods games followed by punishment, reward, or both in the setting of truly repeated games, in which player identities persist from round to round. We show that reward is as effective as punishment for maintaining public cooperation and leads to higher total earnings. Moreover, when both options are available, reward leads to increased contributions and payoff, whereas punishment has no effect on contributions and leads to lower payoff. We conclude that reward outperforms punishment in repeated public goods games and that human cooperation in such repeated settings is best supported by positive interactions with others.

Redefine Statistical Significance

We propose to change the default P-value threshold for statistical significance from 0.05 to 0.005 for claims of new discoveries.

Evaluating replicability of laboratory experiments in economics

Another social science looks at itself Experimental economists have joined the reproducibility discussion by replicating selected published experiments from two top-tier journals in economics. Camerer et al. found that two-thirds of the 18 studies examined yielded replicable estimates of effect size and direction. This proportion is somewhat lower than unaffiliated experts were willing to bet in an associated prediction market, but roughly in line with expectations from sample sizes and P values. Science, this issue p. 1433 By several metrics, economics experiments do replicate, although not as often as predicted. The replicability of some scientific findings has recently been called into question. To contribute data about replicability in economics, we replicated 18 studies published in the American Economic Review and the Quarterly Journal of Economics between 2011 and 2014. All of these replications followed predefined analysis plans that were made publicly available beforehand, and they all have a statistical power of at least 90% to detect the original effect size at the 5% significance level. We found a significant effect in the same direction as in the original study for 11 replications (61%); on average, the replicated effect size is 66% of the original. The replicability rate varies between 67% and 78% for four additional replicability indicators, including a prediction market measure of peer beliefs.

Do More Expensive Wines Taste Better? Evidence from a Large Sample of Blind Tastings

Individuals who are unaware of the price do not derive more enjoyment from more expensive wine. In a sample of more than 6,000 blind tastings, we find that the correlation between price and overall rating is small and negative, suggesting that individuals on average enjoy more expensive wines slightly less. For individuals with wine training, however, we find indications of a positive relationship between price and enjoyment. Our results are robust to the inclusion of individual fixed effects, and are not driven by outliers: when omitting the top and bottom deciles of the price distribution, our qualitative results are strengthened, and the statistical significance is improved further. Our results indicate that both the prices of wines and wine recommendations by experts may be poor guides for non-expert wine consumers.

Outrunning the Gender Gap - Boys and Girls Compete Equally

Recent studies find that women are less competitive than men. This gender difference in competitiveness has been suggested as one possible explanation for why men occupy the majority of top positions in many sectors. In this study we explore competitiveness in children, with the premise that both context and gendered stereotypes regarding the task at hand may influence competitive behavior. A related field experiment on Israeli children shows that only boys react to competition by running faster when competing in a race. We here test if there is a gender gap in running among 7-10 year old Swedish children. We also introduce two female sports, skipping rope and dancing, to see if competitiveness is task dependent. We find no gender difference in reaction to competition in any task; boys and girls compete equally. Studies in different environments with different types of tasks are thus important in order to make generalizable claims about gender differences in competitiveness.

Assessing the Robustness of Power Posing No Effect on Hormones and Risk Tolerance in a Large Sample of Men and Women

In a growing body of research, psychologists have studied how physical expression influences psychological processes (see Riskind & Gotay, 1982; Stepper & Strack, 1993, for early contributions to this literature). A recent strand of literature within this field has focused on how physical postures that express power and dominance (power poses) influence psychological and physiological processes, as well as decision making (e.g., Carney, Cuddy, & Yap, 2010; Cesario & McDonald, 2013; Yap, Wazlawek, Lucas, Cuddy, & Carney, 2013). Carney et al. found that power posing affected levels of hormones such as testosterone and cortisol, financial risk taking, and self-reported feelings of power in a sample of 42 participants (randomly assigned to hold poses suggesting either high or low power). We conducted a conceptual replication study with a similar methodology as that employed by Carney et al. but using a substantially larger sample (N = 200) and a design in which the experimenter was blind to condition. Our statistical power to detect an effect of the magnitude reported by Carney et al. was more than 95% (see the Supplemental Material available online). In addition to the three outcome measures that Carney et al. used, we also studied two more behavioral tasks (risk taking in the loss domain and willingness to compete). Consistent with the findings of Carney et al., our results showed a significant effect of power posing on self-reported feelings of power. However, we found no significant effect of power posing on hormonal levels or in any of the three behavioral tasks.

Salivary testosterone change following monetary wins and losses predicts future financial risk-taking

While baseline testosterone has recently been implicated in risk-taking in men, less is known about the effects of changing levels of testosterone on financial risk. Here we attempt to influence testosterone in men by having them win or lose money in a chance-based competition against another male opponent. We employ two treatments where we vary the amount of money at stake so that we can directly compare winners to losers who earn the same amount, thereby abstracting from income effects. We find that men who experience a greater increase in bioactive testosterone take on more risk, an association that remains when controlling for whether the participant won the competition. In fact, whether subjects won the competition did not predict future risk. These results suggest that testosterone change, and thus individual differences in testosterone reactivity, rather than the act of winning or losing, influence financial risk-taking.

Do People Care About Social Context? Framing Effects in Dictator Games

Many previous experiments document that behavior in multi-person settings responds to the name of the game and the labeling of strategies. Usually these studies cannot tell whether frames affect preferences or beliefs. In this Dictator game study, we investigate whether social framing effects are also present when only one of the subjects makes a decision, in which case the frame may only affect preferences. We find that behavior is insensitive to social framing.

Testosterone exposure, dopaminergic reward, and sensation-seeking in young men

To test the relationship between androgen exposure, dopaminergic reward and sensation-seeking, we compared variation in salivary testosterone (T), 2D:4D digit ratio, facial masculinity, Zuckermans sensation-seeking scale (SSS) and the D4 dopamine receptor (DRD4) genes from 98 young men, between the ages of 18 and 23 years. In univariate analyses, both salivary T and facial masculinity were significantly correlated with the SSS boredom susceptibility subscale, while the presence of the 7-repeat allele (7R+) in the dopamine receptor D4 gene was associated with the SSS thrill and adventure-seeking and overall sensation-seeking. Neither left nor right 2D:4D digit ratio was associated with any sensation-seeking scale. In multivariate models, salivary T and facial masculinity were significant predictors of SSS boredom susceptibility, while 7R+ was a significant predictor of SSS thrill and adventure-seeking. For overall SSS, both 7R+ and salivary T were significant predictors. There was no significant interaction of 7R+ and androgen exposure for SSS or any of the SSS subscales. These results add to earlier reports of an association between T and sensation-seeking. In addition, our results also indicate that genetic variation in DRD4 is independently associated with SSS sensation-seeking.