Geography, Uncertainty, and Polarization

Using new data on roll-call voting of U.S. state legislators and public opinion in their districts, we explain how ideological polarization of voters within districts can lead to legislative polarization. In so-called “moderate” districts that switch hands between parties, legislative behavior is shaped by the fact voters are often quite heterogeneous: the ideological distance between Democrats and Republicans within these districts is often greater than the distance between liberal cities and conservative rural areas. We root this intuition in a formal model that associates intra-district ideological hetero- geneity with uncertainty about the ideological location of the median voter. We then demonstrate that among districts with similar median voter ideologies, the difference in legislative behavior between Democratic and Republican state legislators is greater in more ideologically heterogeneous districts. Our findings suggest that accounting for the subtleties of political geography can help explain the coexistence of polarized legislators and a mass public that appears to contain many moderates

本研究借助涵盖美国州议员唱名投票（roll-call voting）记录及其所属选区公众舆论数据的全新数据集，阐释了选区内部选民的意识形态极化（ideological polarization）如何引发立法极化（legislative polarization）。在所谓的两党轮替的温和选区（moderate districts）中，议员的立法行为往往由选民群体的高度异质性所塑造：这些选区内部民主党与共和党选民的意识形态差距，往往大于自由派城市与保守派乡村之间的意识形态分歧。本研究将这一理论直觉奠基在正式模型之上，该模型将选区内部的意识形态异质性与中位选民（median voter）意识形态定位的不确定性相关联。随后本研究证明，在中位选民意识形态相近的选区中，意识形态异质性越强的选区，其民主党与共和党州议员的立法行为差异就越大。本研究结果表明，充分考量政治地理的细微特质，有助于解释极化立法者与看似存在大量温和派选民的广大民众群体并存的现象。