On the independence of observations between experiments

In experimental economics there exists a lively debate about the independence of observations. Although opinions on the issue differ widely, all concerns regard the independence of subjects' behavior within one session or experiment. This paper attempts to shed some light on the independence of observations between experiments, if they are generated by the same subjects. We analyze experiments with an allocation decision and find that participation in previous experiments tends to increase the amount subjects allocate to themselves. Hence, independence between experiments cannot be presumed if subjects participate repeatedly. The finding has implications for the interpretation of previous allocation decision results and deserves attention when running future experiments. -- experimental methods ; independence of observations ; social preferences ; conditional cooperation