Homogeneous Models and Heterogeneous Voters

<jats:p> Most models assume that voting behaviour can be summarised by a single additive equation. There are good reasons, however, for believing that some voters place more weight on some considerations than others or use different decision rules. In both cases, a single additive equation will produce misleading accounts of the causal processes. Modellers should therefore allow for such differences. In order to illustrate these propositions, I examine evidence from the 2001 British Election Study, which suggests that some voters place more weight on leaders than others. I end by calling for attention to shift from causal complexity to causal diversity. </jats:p>