Lo, S. C. S.(2010).A comparative study of linkage indexes: Co-assignee, reciprocal citation, patent coupling and co-patent.Journal of Library and Information Studies.8(1),11-27.
Fujita, K., Kajikawa, Y., Mori, J., & Sakata, I. (2012). Detecting research fronts using different types of combinational citation. Retrieved August 29, 2015, from http://2012.sticonference.org/Proceedings/vol1/Fujita_Detecting_273.pdf