Two articles contributing to the experimental research about incomplete contracts are analyzed in this paper. Especially interesting is their use of the terms 'firms' and 'workers', although the experiments were performed on students only given information that they were participating in general market experiments. A framework based on Mki (2004) is used both to emphasize what we aim to explain, and by which we explain. Also the concepts of internal and external validity are important. By showing that the articles refer to an external validity which they are not capable of achieving at this moment, their use of 'firms' and 'workers' is found to be questionable. But the two articles are still good examples of experimental research about incomplete contracts.