Stephen A. Jessee

Infuential theories of legislative organization predict that congressional leaders will be selected from the center of their parties. Yet previous research has generally rejected the “middleperson hypothesis,” finding leaders to be extremists. We challenged these findings by testing more‐appropriate null hypotheses via Monte Carlo simulation. We found that congressional leaders (and leadership candidates as a whole) tend to be closer to their party's median than would occur by chance, but leaders also tend to be selected from the left of the median for Democrats and to the right for Republicans. Compared to the pool of announced candidates for leadership positions, winners are not ideologically distinctive. This result suggests that factors affecting the ideology of leaders tend to operate more at the candidate emergence stage.

The theory of spatial voting has played a large role in the development of important results across many areas of political science. Directly testing the foundational assumptions of spatial voting theory, however, has not been possible with existing data. Using a novel survey design, this article obtains estimates of voter ideology on the same scale as candidate positions. The results of this scaling demonstrate that voters possess meaningful ideologies and, furthermore, that these beliefs are strongly related to the sorts of policy proposals considered in Congress. These ideology estimates are then used to uncover the actual relationships between ideology and vote choice for citizens of various types in the 2004 presidential election. Although the choices of independent voters are shown to be largely consistent with the assumptions of spatial voting theory, the decision rules used by partisans differ strongly from what unbiased spatial voting would imply. Although partisans do converge toward the behavior of independents, and hence toward the assumptions of spatial voting theory, as information levels increase, we see that even highly informed partisans show significant differences from what would be implied by unbiased spatial voting theory.