While there may be many different determinants that affect voter turnout in the US, a new study shows there is definitely a correlation between the ease of voting and voter turnout.

Taking into consideration factors such as registration deadlines, voter ID laws and registration restrictions, researchers at Northern Illinois University, Jacksonville University and China's Wuhan University created a "Cost of Voting" index that measures how easy or difficult it was to vote in recent presidential election years.

If you want to focus specifically on the "cost of voting" in the 2016 presidential election, here's a map created by The Washington Post:

According to the study, Oregon was the easiest state to vote in in 2016, which makes sense given that Oregon allows mail-in voting and has implemented automatic voter registration. On the other end of spectrum is Mississippi, the most "difficult" state to vote in the US because of its voting policies, which includes a photo ID requirement at the polls and doesn't allow for early voting.

If you plot out the voter turnout of each state in the 2016 presidential election against its measured "Cost of Voting" index — as The Washington Post has done in this graph below — the correlation seems pretty clear:

With the exceptions of a few outliers, such as Hawaii, which had one of the lowest voter turnouts in the 2016 presidential election despite its relatively lenient voting laws, the graph indicates a negative correlation between the "Cost of Voting" index and voter turnout. In other words — and this probably isn't that surprising — the more inconvenient it was to vote, the lower the voter turnout in 2016.

[The Washington Post]