Although most opposition to implementing a nationwide vote-by-mail option has come from Republican circles, such a system would not advantage either major party, according to a study from Stanford University’s Democracy and Polarization Lab.

Several states, including Colorado, Hawaii, Oregon, Washington and Utah, have mail-in voting as an option, while California gives individual counties the option to implement it. With public health experts recommending against large gatherings during the coronavirus pandemic, advocates have called for the expansion of mail-in voting.

As most states phased the system in on a county-by-county basis, researchers compared results in counties that adopted a program to those within the same state that did not. They did not measure any partisan effect.

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“By comparing counties that adopt a vote-by-mail program to counties within the same state that do not adopt the program, we are able to compare the election outcomes and turnout behavior of voters who have different vote-by-mail accessibility but who have the same set of candidates on the ballot for statewide races,” they wrote.

Comparing county-level election results and public party registration data for California and Utah voters ranging from 1996 to 2018, researchers found “a truly negligible effect” on partisan turnout rates with the addition of a vote-by-mail option, with turnout slightly up across the entire voting-age population.

“Vote-by-mail causes around a 2-percentage-point increase (estimates range from 1.9 to 2.4 percentage points) in the share of the voting-age population that turns out to vote,” the study says.

Although earlier studies have had similar results, the Stanford research “permits a stronger research design than was previously possible and ... our data set runs through the 2018 midterm elections, allowing for the most up-to-date analysis available,” the authors wrote.

Opponents of voting by mail have frequently argued it would disadvantage Republicans. President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE, one of its most vocal opponents, has said it would mean “you’d never have a Republican elected in this country again,” and Georgia House Speaker David Ralston (R) said it would be “extremely devastating to Republicans and conservatives in Georgia,” according to the Atlanta Journal-Constitution.