The evolution and formation of amicus curiae networks

This paper sheds light on two age-old questions of interest group behavior: how have interest group coalition strategies changed over time and which factors determine whether interest groups work together? Through the creation of a new network measure of interest group coalitions based on cosigner status to United States Supreme Court amicus curiae briefs, we illuminate the central players and overall characteristics of this dynamic network from 1930 to 2009. We present evidence of an increasingly transitive network resembling a host of tightly grouped factions and leadership hub organizations employing mixed coalition strategies. We also model the attribute homophily and structure of the present-day network. We find assortative mixing of interest groups based on industry area, budget, sales and membership.

► We create a new network measure of interest group coalitions from 1930 to 2009.
► Average interest group degree and betweenness centrality have increased.
► There is a negative pattern over time in density, transitivity and centralization.
► ERGM shows many regions of tight association and the overall network is segmented.