done by KALISH, MILNOR, NASH, and NERING [1954]. Today the use of experiments in controlled laboratory settings has become widespread. Earlier, economists went into the field to observe phenomena as the behavior of individuals, corporations and nations in action, then they formulated theories to explain what they saw. But unlike natural scientists, economists have not been able to test their theories under controlled conditions. Now experimental economists are able to replicate their results. Replication is very proble­ matic for field studies, because rarely the same conditions can be established again. Moreover, experimenters are able to test theories for situations described by simplified models which are not observable in the real world.