@unpublished{publication-5750,
	author={Frey, Bruno S and Meier, Stephan},
	institution={University of Zurich},
	issn={1424-0459},
	number={No. 107},
	series={Working paper series / Institute for Empirical Research in Economics},
	title={Pro-Social Behavior, Reciprocity or Both?},
	year=2002,
}