Replication Data for: Legislature Size and Party Unity: Evidence from Historical U.S. State Legislatures

The size of a legislature is one of its most fundamental features, yet there is little consensus on how large legislatures should be. Further, many modern-day reformers are dissatisfied with the current size of American legislatures. We explore the effect of legislature size on party unity, which is important for policy outcomes and is plausibly shaped through both individual and collective incentives affected by legislature size. To test this relationship, we use original roll call data from the Illinois House of Representatives in the mid-nineteenth century, which dramatically changed size twice in this period. Using Indiana as a control, we show that larger chambers are associated with lower party unity, and that this change is likely due to intra-legislature dynamics rather than legislator-constituent relationships. We demonstrate that our results extend to more-modern periods by using additional data from Vermont and New Jersey.

立法机构规模是其最核心的特征之一，但学界对于立法机构的最优规模尚未达成共识。此外，诸多当代改革者对美国立法机构的现有规模并不满意。本研究探讨立法机构规模对党派凝聚力的影响：该指标对政策产出至关重要，其形成可能受立法机构规模所影响的个体与集体激励机制共同作用。为验证这一关联，我们采用19世纪中期伊利诺伊州众议院的原始点名投票（roll call）数据，该时期内众议院规模曾两次大幅调整。我们以印第安纳州作为对照组，研究发现议院规模越大，党派凝聚力越低，且这一变化更可能源于立法机构内部的动态机制，而非议员与选民的关联。通过使用佛蒙特州与新泽西州的额外数据，我们进一步证明，上述结论可推广至更近代的时期。