The Conservative Policy Bias of US Senate Malapportionment

The US Senate is unique in the United States and rare internationally for its total disregard of population differences among its representational units. To analyze malapportionment’s policy impact, we devised a hypothetical reapportionment scheme that more closely approximates state population but remains favorable to small states. We developed a formula to reweight senators’ roll-call votes to reflect better state population differences. We recalculated 804 key US Senate votes between 1961 and 2019 and found that state equality in the Senate systematically biases policy outcomes toward Republican preferences.