Multi-issue coalitions in the Congress [voting alignments on supercomputer]

The authors explore voting alignments in six US Senates between 1959 and 1981. The authors´ thesis is that the Senate is organized by four recurring multiissue coalitions that combine in various ways to form larger voting coalitions. The four-coalition hypothesis was tested with the use of complete-link hierarchical clustering on a matrix of senators over contested bills. The significance of clustering into four rather than some other number of groups was established by computing gamma goodness-of-fit statistics for each possible clustering, a computation that was practical only with the aid of a supercomputer. Beyond the basic clustering result, descriptive statistics were used to measure membership consistency over time. Membership in the four coalitions persisted even across Senates spanning the supposed Reagan realignment. This finding and others support the conclusion that the multiissue coalition is the appropriate unit in roll-call analysis