Do Ideological Preferences Explain Parliamentary Behaviour? Evidence from Great Britain and Canada
Are parliamentary parties cohesive because leaders successfully impose discipline on their MPs or because MPs prefer - hence support - the same policies as their leaders do? If the latter is correct, and party cohesion is produced largely by members' concordant preferences, then models that explain cohesion as a function of the disciplinary mechanisms available to parties once the MP is in Parliament (for example, the distribution of patronage or the threat of de-selection) are not useful. This article uses British and Canadian MPs' responses to candidate surveys to estimate MPs' positions on a variety of ideological dimensions and then shows that MPs' preferences on these ideological dimensions only partially explain how often they vote against their parties. Indeed, even after one controls for an MP's ideological preferences, party affiliation remains a powerful predictor of the MP's loyalty or dissent - suggesting that party discipline does, in fact, contribute to cohesion. Additional tests indicate that these results are not spurious.