 During the last four decades, Batson and his collaborators have systematically explored these egoistic hypotheses and many others. Their strategy is to design experiments in which the altruistic explanation of the link between empathy and helping can be compared to one or another specific egoistic explanation. Reviewing all of these experiments would require a far longer  entry.[16]  Instead the focus will be on two clusters of experiments that illustrate the potential philosophical rewards of designing and interpreting experiments in this area, as well as some difficulties with the project.