Explaining Parliamentary Party Cohesion : Can Psychology Help ?

Parliaments in most established democracies are characterised by high levels of political party cohesion in voting. Political scientists tend to explain this behaviour in terms of individual incentives, implicitly or explicitly applying a logic of rational choice. Cohesion is linked to discipline, and the powers available to party whips: for example control over resources, reselection opportunities, and positions in government. This analysis has however been questioned through a study of the British House of Lords conducted by Philip Norton (2003). The House of Lords provides an example of ‘cohesion without discipline’, as parties vote almost uniformly together despite whips enjoying none of the aforementioned powers. Since members gain seats in the chamber for life, cannot be removed, and are often nearing the end of their careers, rational self-interest provides little reason to vote together. Alternative explanations are therefore needed. This paper makes some first attempts to provide such explanations. Drawing on data from a survey of members of the House of Lords, it tests alternative reasons for cohesion based on psychological theories. In particular it draws on ideas from social identity theory to test the effect of members’ attitudes of ‘groupishness’ to their voting behaviour. Our results suggest that group effects as understood by social identity theorists play an important role in explaining party cohesion. Through testing in the (perhaps uniquely) discipline-free arena of the House of Lords, these results provide the foundations for a future research agenda to explain cohesion in parliaments more widely. This is an exploratory work, not intended to be a fully finished product. Comments on any aspect of the paper are welcomed by the author. Please do not cite this paper without the author’s explicit permission.