The relationship between coalition policy and party policy

The recent availability of multidimensional interval level data on the policy positions of most European political parties opens the way for a more sophisticated development and testing of policy-based coalition theories. This paper considers some of the conceptual and operational problems involved in dealing with notions such as the "policy package" of a coalition, the "policy distance" between two points in policy space, and the "aggregate policy distance" of a group of parties. It shows that party-specific perceptions of the salience of issue dimensions can have a considerable impact on the predictions of the theories concerned, which deal with coalition membership, coalition payoffs and coalition policy.