The Institutionalization of State Communities of Organized Intersts

examine the diversity of interest communities on two dimensions: the range of substantive interests and organizational types represented. The former has remained quite stable over the last two decades while the level of relative institutional representation has increased markedly We repli-cate and extend Lowery and Gray's (1998) analysis of four theoretical accounts of temporal and spatial variations in levels of the latter-insti-tutional dominance. Only one of their four accounts-one emphasizing the role of interest system density in promoting direct lobbying by insti-tutions-survives these tests. We conclude by discussing the implications of these findings for interest group politics. The diversity of interest group communities can be evaluated in terms of any number of criteria. Historically, however, we have been interested in diversity with respect to two dimensions. By far, the overwhelming portion of the literature on interest system diversity has concerned the range and distribution of substantive interests. Among many others, Schattschneider (1960), Schlozman and Tierne