A polling station in Milwaukee. Voter turnout was relatively high across Wisconsin, but down significantly across most of the country. Darren Hauck / Getty Images

The turnout for Tuesday general election was the lowest recorded level since World War II, according to the United States Election Project. A scant 36.4 percent of the voting-eligible population cast ballots last week, marking the smallest percentage participation since 1942, when less than 34 percent went to the polls.

Voter participation has generally been in decline since the early 1960s. Years with presidential elections usually see higher turnout than midterm election cycles — 62 percent voted in the 2008 election, 58 percent in 2012 — but 2014 was down substantially, even when compared with the last two off-year elections (41 percent voted in 2010).

Read more of Al Jazeera America's 2014 election coverage

Measuring the motivations behind voter turnout is not an exact science. Decisions might be based on convenience or logistics — a voter might not be able to take time off work or lacks adequate transportation to make it to a polling place — or it might be a byproduct of interest-level or alienation — there might not be a competitive, high-profile contest or voters might have just lost faith in their elected officials or the electoral process.

Or, as has been the case with increasing frequency in the wake of the Supreme Court’s Shelby decision, the rules may have changed enough to confuse voters or create real barriers to participation.

Making a decision about whether or not to vote “is a puzzle about many factors,” said Bernard Fraga, assistant professor of political science at Indiana University in Bloomington. But Fraga noted, “The trend has been more towards implementing measures that are imposing regulations or shortening the number of hours you can vote early and registering voters.”

With that in mind, The Brennan Center for Justice at New York University Law School has undertaken to compare 2014 midterm turnout with previous elections to understand how many potential voters might have been affected by voting-law changes. Brennan then measured turnout against margins of victory in an attempt to discern whether changes in turnout might have altered the results.