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：众议院选区的划分由许多美国州的党派行为者决定，这引发了关于选区不合理划分的担忧。为了分离选区重划的党派影响和其他因素（包括地理和选区重划规则）的影响，我们将实施计划的可能党派组成与一组模拟的替代计划进行比较，这些计划作为非党派基准。我们发现，2020年选区重划周期中存在广泛的党派选区不合理划分，但其大部分造成的选举偏见在全国范围内被抵消，在平均情况下使共和党人多得两个席位。地理和选区重划规则分别提高了适度的亲共和党偏见。最后，我们发现，党派选区不合理划分降低了选举竞争性，并使众议院的党派组成对全国投票的变化反应变得不太敏感。