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Estimating Brexit Ideal Points in the House of Lords

Thu, August 29, 2:00 to 3:30pm, Marriott, Wilson C


The debate over the United Kingdom’s relationship with the European Union, following the success of the Leave side in the 2016 referendum, has been the most important political and constitutional issue in British politics in several decades. While the House of Commons has the dominant role in shaping Brexit, members of the House of Lords have influence on the process due the volume of legislation needed to implement the United Kingdom’s withdrawal from the European Union and the compressed time frame in which that legislation must be adopted. In this paper, I estimate ideal points on Brexit for each member of the House of Lords based on their votes on amendments to Brexit-related legislation following the 2016 referendum. Using a Bayesian hierarchical ideal point model, peers’ Brexit ideal points are modeled as a function of their demographic, professional, and party political characteristics. This approach produces estimates of Brexit ideal points that are highly predictive of voting behavior both among peers belonging to the major party groups and among Crossbench peers. Using these estimates, one can calculate the probability that a peer is the median voter on Brexit, and the likelihood that the result a Brexit-related division in the House of Lords would have been reversed if all peers had voted. Moreover, the results demonstrate that peers’ preferences on Brexit are systematically related to demographic characteristics such as gender, and professional characteristics such as prior service as a member of the House of Commons and the nature of their appointment to the House of Lords. By identifying the underlying structure of Brexit-related preferences in the House of Lords, these findings both help to explain the behavior of peers in the Brexit process thus far and provide insight into the role that the Lords is likely to play in the United Kingdom’s future relationship with Europe, which is likely to remain a salient issue in British politics for years to come. Moreover, it makes a broader contribution to the study of legislative behavior by explaining variation in preferences among legislators detached from the traditional electoral incentives that typically drive legislators' actions.