This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).

This article has been retracted at the request of the Editor-in-Chief and co-Editors, as it contain portions of other authors' writings on the same topic in other publications, without sufficient attribution to these earlier works being given. The principal authors of the paper acknowledged that text from background sources was mistakenly used in the Introduction without proper reference to the original source. Specifically, the first page and a half of the article (pp. 2177–2178) contain together excerpts from Wikipedia (first paragraph), Wasserman and Faust's “Social Network Analysis: Methods and Applications” (pp. 17–20) ISBN 10: 0-521-38707-8; ISBN 13: 978-0-521-38707-1. Publication Date: 1994, and W. de Nooy, A. Mrvar and V. Bategelj's “Exploratory Social Network Analysis with Pajek"” (pp. 31, 36, 123, and 133) ISBN 10: 0-521-60262-9; ISBN 13: 978-0-521-60262-4. Publication Date: 2005.

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One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. The re-use of material, without appropriate reference, even if not known to the authors at the time of submission, breaches our publishing policies.