Gerald Holton «Robert K. Merton - Biographical Memoirs». Proceedings of the American Philosophical Society, 148, 4, 04-12-2004, pàg. 506–517 [Consulta: 7 agost 2007]. «He developed a theory of the reference group (i.e., the group to which individuals compare themselves, which is not necessarily a group to which those individuals belong), and elaborated on the concepts of in-group and out-group.»