Interest groups: a survey of empirical models that try to assess their influence

Substantial political power is often attributed to interest groups. The origin of this power is not quite clear, though, and the mechanisms by which influence is effectuated are not yet fully understood. The last two decades have yielded a vast number of studies which use empirical models to assess the importance of interest groups for the formation of public policy. Each of these studies yields insights on particular, confined aspects of interest group politics. To get a more complete picture of the results, however, a broad survey of the literature seems useful. It is the purpose of this paper to provide such a survey.