The Policy Role of Sub-Party Coalitions

Abstract

This is a progress report on a study of the policy role of subparty coalitions in nine U.S. Senates between 1959 and 1988 and ultimately both houses of Congress since 1948. Our hypothesis is that policy is determined by the actions of a small number of subparty coalitions that combine in various ways to form larger policy determining 'voting' coalitions. The subparty coalitions were identified by applying complete-link hierarchical clustering (Baker and Hubert, 1976) to a matrix of Senators over contested bills. Significant groups were defined by the location of stress elbows after computing gamma goodness-of-fit statistics for each possible clustering, a computation that was practical only with the aid of a supercomputer. The result identified groups with memberships substantially overlapping those of subparty coalitions long observed by journalists and other close observers of the Congress. These groups became the unit of analysis for examining the treatment of all contested bills and amendments within each Senate, the consistency of subparty coalition membership across Senates. Subparty coalitions were active in over ninety percent of the winning voting coalitions, and membership remained stable through the period investigated. The implications of these and other findings for using formal coalition theory and interpreting the policy roles of political parties, ideology, policy dimensions and individualistic behavior on public policy are explored.