David Lazer Ines Mergel Curt Ziniel Kevin Esterling Michael Neblo Members of congress websites: diffusion at the tip of the iceberg. 26-34 2007 conf/dgo/2007 DG.O http://doi.acm.org/10.1145/1248460.1248466 db/conf/dgo/dgo2007.html#LazerMZEN07