Writing in The New York Times to summarize their recent paper, scholars Charlotte Hill and Jacob Grumbach have looked at the impact of same-day voter registration laws, which let voters register at the same time they cast a ballot, and have concluded that the policy is one of the most effective ways to improve voter turnout.

The study relied on the Census Bureau's Current Population Survey Voter Supplement, which is a large-scale statistical sample of the country. The researchers compared voters in states that do allow same-day registration with demographically similar Americans living in states that do not.

The analysis shows that same-day registration laws would increase turnout in a presidential electorate, a result consistent with those of other studies, and it specifically finds the largest increase among young voters. The authors lay out the ways in which registration laws disproportionately burden younger people, since they are much more likely to change addresses and thus have to reregister each time.

In particular, the study estimates that presidential election turnout among those ages 18 to 24, typically the group with the lowest turnout, could surge from 30% to as much as 40% with same-day registration. While older voters would be more likely to turn out, too, the share of the electorate that is over 35 years old could fall by more than 2%. Consequently, the authors conclude that turnout would become more demographically reflective of the citizenry along the lines of age, race, and income, in turn making it more Democratic.

Looking specifically at Michigan in 2016, which Donald Trump won by just shy of 11,000 votes, Hill and Grumbach conclude that same-day registration would have flipped the state to Hillary Clinton by producing a net gain of 90,000 Democratic votes. Michigan voters enacted same-day registration by ballot initiative in 2018, so the researchers will be able to re-evaluate their analysis after the 2020 elections to review its impact there.