Before we can apply organizational theories to social aggregates, their status as entities must be evaluated. The degree to which a social aggregate is a system may be assessed using common fate, similarity and proximity as variables which indicate “systemicity”. The degree to which an organization behaves as an entity is related to its “decomposability” as a hierarchical system (Simon, 1962) and to how “loosely coupled” (Weick, 1976) it is. A nested analysis of variance technique provides an empirical illustration of the entitativity (degree of being an entity) of a number of systems with respect to measures of control and indicates the appropriate level of analysis for any organizational study using these data. The nested analysis of variance technqiue and the idea of entitativity are discussed in light of the contributions they make to selection of the appropriate unit of analysis, to the problem of loosely coupled systems and finally to the ability to uncover the appropriate level of analysis for studying organizations. We contend that the entitativity of social aggregates is a matter for empirical investigation and not only for a priori definition.