Congressional district lines in many U.S. states are drawn by partisan actors, raising concerns about gerrymandering. To separate the partisan effects of redistricting from the effects of other factors including geography and redistricting rules, we compare possible party compositions of the U.S. House under the enacted plan to those under a set of alternative simulated plans that serve as a non-partisan baseline. We find that partisan gerrymandering is widespread in the 2020 redistricting cycle, but most of the electoral bias it creates cancels at the national level, giving Republicans two additional seats on average. Geography and redistricting rules separately contribute a moderate pro-Republican bias. Finally, we find that partisan gerrymandering reduces electoral competition and makes the partisan composition of the U.S. House less responsive to shifts in the national vote.

翻译：美国许多州的国会选区边界由党派行为者划定，引发了关于选区划分不公的担忧。为区分选区重划的党派效应与地理因素及选区划分规则等其他因素的影响，我们将现行选区划分方案下可能产生的美国众议院政党构成，与一组作为无党派基线的替代模拟方案下的情况进行比较。我们发现，2020年选区重划周期中党派选区划分现象普遍存在，但其产生的选举偏差在全国层面基本相互抵消，平均为共和党增加了两个席位。地理因素与选区划分规则分别带来适度的亲共和党偏差。最后，我们发现党派选区划分降低了选举竞争性，并使美国众议院的政党构成对国家投票格局的变化敏感度降低。