“…Some of the more recent analyses have tried to assess the reasons why political actors establish contacts to some actors but not to others. Particularly ideology (Henry et al, 2010;Laumann et al, 1992), preference similarity on political issues (Weible and Sabatier, 2005;Zafonte and Sabatier, 1998;König 1 and Bräuninger, 1998;Carpenter et al, 2004), preference dissimilarity (Stokman and Zeggelink, 1996;Stokman and Berveling, 1998), functional or institutional interdependence (Zafonte and Sabatier, 1998;König and Bräuninger, 1998), social trust (Carpenter et al, 2004;Henry et al, 2010) and perceived influence (Weible and Sabatier, 2005;Stokman and Zeggelink, 1996;Stokman and Berveling, 1998) have been found to be drivers of tie formation in policy networks. These findings have been obtained by conducting quantitative case studies of several policy domains or subsystems like San Francisco Bay-Delta water policy (Zafonte and Sabatier, 1998), California marine protected area policy (Weible and Sabatier, 2005), the U.S. health policy and energy policy sectors (Carpenter et al, 2004;Laumann et al, 1992), U.S. agricultural policy and labor policy (Laumann et al, 1992), and the German labor policy domain (König and Bräuninger, 1998).…”