Abstract. Experimentalists frequently claim that human subjects in the laboratory violate game-theoretic predictions. It is here argued that this claim is usually premature. The paper elaborates on this theme by way of raising some conceptual and methodological issues in connection with the very definition of a game and of players ’ preferences, in particular with respect to potential context dependence, interpersonal preference dependence, backward induction and incomplete information.

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Departures from pure self interest in economic experiments have recently inspired models of "social preferences". We conduct experiments on simple two-person and three-person games with binary choices that test these theories more directly than the array of games conventionally considered. Our experiments show strong support for the prevalence of "quasi-maximin" preferences: People sacrifice to increase the payoffs for all recipients, but especially for the lowest-payoff recipients. People are also motivated by reciprocity: While people are reluctant to sacrifice to reciprocate good or bad behavior beyond what they would sacrifice for neutral parties, they withdraw willingness to sacrifice to achieve a fair outcome when others are themselves unwilling to sacrifice. Some participants are averse to getting different payoffs than others, but based on our experiments and reinterpretation of previous experiments we argue that behavior that has been presented as "difference aversion" in re...

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We examine, experimentally and theoretically, how communication within a partnership may mitigate the problem (highlighted in contract theory) of hidden action. What is the form and content of the communication? Which model of decision-making can capture the impact of communication? We consider free-form communication, measure beliefs (about actions and beliefs), and examine which motivational forces influence subjects. We find they harbor belief-dependent preferences that can be captured using psychological game theory. In particular, agents are influenced by guilt aversion, which suggests a theory of why and how communication influences behavior in which statements of intent and resulting expectations play a special role. This has bearing on how to understand partnerships and contracts.

Online labor markets have great potential as platforms for conducting experiments. They provide immediate access to a large and diverse subject pool, and allow researchers to control the experimental context. Online experiments, we show, can be just as valid—both internally and externally—as laboratory and field experiments, while often requiring far less money and time to design and conduct. To demonstrate their value, we use an online labor market to replicate three classic experiments. The first finds quantitative agreement between levels of cooperation in a prisoner’s dilemma played online and in the physical laboratory. The second shows – consistent with behavior in the traditional laboratory – that online subjects respond to priming by altering their choices. The third demonstrates that when an identical decision is framed differently, individuals reverse their choice, thus replicating a famed Tversky-Kahneman result. Then we conduct a field experiment showing that workers have upwardsloping labor supply curves. Finally, we analyze the challenges to online experiments, proposing methods to cope with the unique threats to validity in an online setting, and examining the conceptual issues surrounding the external validity of online results. We conclude by presenting our views on the potential role that online experiments can play within the social sciences, and then recommend software development priorities and best practices. ∗Thanks to Alex Breinin and Xiaoqi Zhu for excellent research assistance. Thanks to

CentER and CentERdata is gratefully acknowledged. We thank Hanneke Dam, Marcel Das and Corrie Vis of

Abstract: In some experiments rational players who understand the structure of the game could improve their payoff. We bound the size of the observed losses in several such experiments. To do this, we suppose that observed play resembles an equilibrium because players learn about their opponents ’ play. Consequently, in an extensive form game, some actions that are not optimal given the true distribution of opponents ’ play could be optimal given available information. We find that average losses are small: $0.03 to $0.64 per player with stakes between $2 and $30. In one of the three experiments we examine this also implies a narrow range of outcome.

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