The focus for the Centre is research into individual and strategic decision-making using a combination of theoretical and experimental methods. On the theory side, members of the Centre investigate individual choice under uncertainty, cooperative and non-cooperative game theory, as well as theories of psychology, bounded rationality and evolutionary game theory. Members of the Centre have applied experimental methods in the fields of public economics, individual choice under risk and uncertainty, strategic interaction, and the performance of auctions, markets and other economic institutions. Much of the Centre's research involves collaborative projects with researchers from other departments in the UK and overseas. Abstract:Psychological game theory can provide rational-choice-based framing effects; frames influence beliefs, beliefs influence motivations. We explain this theoretically and explore empirical relevance experimentally. In a 2×2 design of one-shot public good games we show that frames affect subject's first-and second-order beliefs, and contributions. From a psychological gametheoretic framework we derive two mutually compatible hypotheses about guilt aversion and reciprocity under which contributions are related to second-and first-order beliefs, respectively. Our results are consistent with either.Keywords: framing; psychological game theory; guilt aversion; reciprocity; public good games; voluntary cooperation JEL codes: C91, C72, D64, Z13.Acknowledgments: This paper is part of the MacArthur Foundation Network on Economic Environments and the Evolution of Individual Preferences and Social Norms. Support from the EU-TMR Research Network ENDEAR (FMRX-CT98-0238) and the University of St. Gallen Grundlagenforschungsfonds is gratefully acknowledged. Part of the research was done when Martin Dufwenberg visited Bonn University on a F. W. Bessel Research Award from the Alexander-von-Humboldt Foundation and part when he later on was supported by the NSF. Simon Gächter is grateful for the hospitality he enjoyed at the Institute of Advanced Studies at Hebrew University (Jerusalem) while working on this paper. We thank Christian Thöni for very helpful research assistance. We are grateful for comments from Pierpaolo Battigalli, Colin Camerer, Gary Charness, Glenn Harrison, Eva Poen, Lisa Rutström, Arthur Schram, Martin Sefton, Jean-Robert Tyran, Manuela Vieth, and many seminar participants. Finally, our thanks go to an anonymous referee for many helpful comments and suggestions.

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Abstract This paper contributes to the ongoing methodological debate on context-free versus in-context presentation of experimental tasks. We report an experiment using the paradigm of a bribery experiment. In one condition, the task is presented in a typical bribery context, the other one uses abstract wording. Though the underlying context is heavily loaded with negative ethical preconceptions, we do not find significant differences. We conjecture that the experimental design transmits the essential features of a bribery situation already with neutral framing, such that the presentation does not add substantially to subjects' interpretation of the task. Terms of use: Documents in KeywordsCorruption, context, framing, valence, experimental instructions, laboratory, trust, reciprocity, ethical behaviour, social norms JEL Classification CodesC91, D62, D72, D73, K42 AcknowledgementsThe authors thank Heiko Schmidt for valuable research assistance, Bernd Irlenbusch, Elke Renner, Reinhard Selten, and seminar participants in Amsterdam, Wittenberg and Strasbourg for helpful comments and suggestions. All errors remain our own. Financial support by the European Union through the TMR research network EN-DEAR (FMRX-CT98-0238) is gratefully acknowledged.

We analyze how physicians, medical students, and non-medical students respond to financial incentives from fee-for-service and capitation. We employ a series of artefactual field and conventional lab experiments framed in a physician decision-making context. Physicians, participating in the field, and medical and non-medical students, participating in lab experiments, respond to the incentives in a consistent way: Significantly more medical services are provided under fee-for-service compared to capitation. Our findings are robust regarding subjects' gender, age, and personality traits.

Standard-Nutzungsbedingungen:Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden.Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen.Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in

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We present a field experiment to assess the effect of own and peer wage variations on actual work effort of employees with hourly wages. Work effort neither reacts to an increase of the own wage, nor to a positive or negative peer comparison. This result seems at odds with numerous laboratory experiments that show a clear own wage sensitivity on effort. In an additional real-effort laboratory experiment we show that explicit cost and surplus information that enables to exactly calculate employer's surplus from the work contract is a crucial prerequisite for a positive wage-effort relation. This demonstrates that employee's reciprocity requires a clear assessment of the surplus at stake. Keywordsefficiency wage, reciprocity, fairness, field experiment, real effort JEL Codes C91, C92, J41 AcknowledgementsWe thank Heidi Schrader and Anke Schmalenbach for research assistance. We thank Ernst Fehr, Reinhard Selten, and three anonymous referees for helpful comments. We are grateful for comments and suggestions on our work by participants

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