Imagine a large ISS study where the analyses are based on study pools that represent sets of subjects having specific attributes of clinical interest. For example, a study pool might identify subjects belonging to several component core studies or, perhaps, a specific indication, such as COPD or epilepsy. Conversely, the study pool might exclude certain subjects, such as those subjects who took the study drug in the core study but not in the followup study. Whatever the criteria, the study pools are well-defined. Moreover, the study pool might not be mutually exclusive; that is, a subject can be found in more than one study pool. Consequently, a single study might contribute to more than one study pool, such as the subjects in Study ABC001 contributing to Study Pools SP01 and SP03.