Estimating the Effect of Nonseparable Preferences in Eu Treaty Negotiations

This article derives theoretical expectations about the importance of nonseparable preferences at EU treaty negotiations. It argues that member states’ positions on the degree of integration depend on the expected reform of the decision rule and vice versa. This nonseparability effect varies across member states. Wealthier member states (net payers) would prefer a more majoritarian and efficient decision rule when confronted with a higher level of vertical integration. The overall size of the nonseparability effect can be explained by the policy area-specific degree of preference asymmetry. In order to test these expectations the article advances existing statistical models of ideal point estimation and derives a model that allows for an explicit estimation of nonseparability effects. It applies this model to data on member states’ positions at the IGC 2003—4. The two-stage estimator presented in this article may be considered useful in other applications of ideal point estimators.