Backstrom, L.; Huttenlocher, D. P.; Kleinberg, J. M. & Lan, X. (2006), Group formation in large social networks: membership, growth, and evolution., in Tina Eliassi-Rad; Lyle H. Ungar; Mark Craven & Dimitrios Gunopulos, ed., 'KDD' , ACM, , pp. 44-54 .