Gerald Holton (4 December 2004). "Robert K. Merton - Biographical Memoirs". Proceedings of the American Philosophical Society148 (4): 506–517. http://www.amphilsoc.org/sites/default/files/proceedings/480411.pdf. பார்த்த நாள்: 2007-08-07. "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".