Ullmann (1985) described this body of research as “Data in Search of a Theory” and a dozen years later, Griffin and Mahon (1997) entitled their review as “twenty-five years of incomparable research.” The question remains without a definitive answer. The observed differences in findings across the three groups of papers do not necessarily reflect mistakes or inaccuracies, but, most often, differences in perspective such as observation periods, sample firms, measures of corporate performance and methodological approaches for the empirical analysis (Becchetti et al. 2005a).