Sun. Oct 2nd, 2022
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With an uncontrolled pandemic raging, many states have considered moving to a postal voting system. That has proved politically controversial, as President Trump has submitted evidence-free claims that it will lead to massive fraud or provide some other unspecified benefit to Democrats. Meanwhile, proponents of postal voting sometimes present it as the solution to US citizens’ generally low electoral participation. Voting by post, they say, will significantly increase turnout.

Two researchers decided this was something they could answer. Michael Barber of BYU and John Holbein of the University of Virginia took advantage of states where voting was rolled out by mail by county. Their results suggest that voting by mail offers neither party an advantage, but it also hasn’t done much to boost participation.

A tale of two states

The work is based on voter records and census data from two states that voted by mail, but did not roll it out uniformly across the state. Instead, Utah and Washington both had different counties that adopted the system at different times, providing a shifting set of experimental and control conditions. The two states balance each other nicely, as they can be seen as something akin to mirror images. Eastern Washington is largely rural and conservative, but state politics is dominated by the urbanized coastal region. In Utah, while the Salt Lake City area is somewhat liberal, conservative politics dominate the state.

The challenge for the job is that every election has a unique dynamic, so you would expect some background of change going on beyond the rollout of postal voting. To address this, Barber and Holbein perform what is called a difference-in-difference analysis. This form of analysis tracks the changes in each province in the elections and compares those differences with the differences in other provinces. Ideally, this will largely explain the differences between the elections, with the only noticeable difference being caused when individual provinces made the switch to postal voting.

However, there are multiple ways to implement difference-by-difference analysis, and the researchers tried a number of different mathematical models on their data. They have also broken down matters at the provincial level using individual voting data and census data.

When it comes to turnout, the effects of postal voting are small, but positive. Depending on the model used, turnout increases by 1.8 to 2.9 percentage points, an effect that is statistically significant.

A tale of two parties

But there was no indication that either side would benefit from this increased turnout. Here you can see the authors’ approach as the opposite of p hacking: they tried a variety of models and failed to find a statistically significant effect in any of them, leaving them confident in the negative result. While the average of the models represents a 0.7 percentage point increase in Democratic voter share, confidence intervals run to negative numbers, meaning it could just as easily increase Republican share.

“To us it seems possible, perhaps even probable,” suggested Barber and Holbein, “that VBM will bring in individuals who are hesitant to vote, and there are plenty of individuals in both political parties.”

There are certainly nits to pick with this study. While Utah and Washington are great for balancing liberal/conservative issues, they are certainly not representative of the US demographic as a whole. And it’s possible that there are some subtle demographic differences associated with the adoption of mail votes in each county in these states. But it’s unlikely we’ll do much better than this analysis, and we certainly won’t until critical decisions about this year’s election are made. So when states debate what to do, they should do so knowing that the best available evidence suggests that voting by mail offers no partisan benefits.

scientific progress2020. DOI: 10.1126/sciaadv.abc7685 (About DOIs).

By akfire1

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