We run a public good experiment in the field and in the lab with (partly) the same subjects. The field experiment is a … true natural field experiment as subjects do not know that they are exposed to an experimental variation. We can show that … subjects' behavior in the classic lab public good experiment correlates with their behavior in the structurally comparable …

To investigate the external validity of laboratory results, we combine a public good experiment with three treatments … in a field experiment. One treatment offers the opportunity to free-ride, the other two are placebo treatments. We …