At a Wednesday town hall event in Cleveland, President Obama came very close to saying the US should make it illegal not to vote, like Australia does:

Obama plugs mandatory voting: "It would be transformative if everybody voted," he says, citing Australia-style voting. — jennifer bendery (@jbendery) March 18, 2015

This isn't an outright endorsement, though the right-leaning Washington Times quotes Obama as saying that compulsory voting "may end up being a better strategy in the short term" than limiting campaign donations.

But it's certainly a surprising thing to hear the president say. Eleven countries — including Australia, Singapore, and Brazil — enforce compulsory voting laws, and another 11 have them on the books but don't enforce them. But politicians and commentators in the US rarely mention the idea. But it's worth taking the proposal seriously. Other plans to increase turnout — like holding elections on weekends, making Election Day a national holiday, or having everyone vote by mail — have had mixed results; some studies say they work, others find no or even negative effect.

Compulsory voting, on the other hand, definitely works.

Compulsory voting increases turnout

Stanford's Simon Jackman, reviewing the evidence in 2001, found that compulsory voting (usually enforced by fines, or loss of government benefits) increases turnout, with country comparisons indicating a boost of 7-17 percentage points.

The experiences of individual countries adopting or repealing compulsory voting laws also suggest a significant effect. For example, turnout in the nine elections after Australia adopted compulsory voting was, on average, 94.6 percent, compared to a 64.2 percent average for the nine elections before the reform. In the absence of experimental evidence, it's hard to be too confident about the exact size of the effect, but the research base — including studies released after Jackman's review — is fairly unanimous that compulsory voting increases turnout.

And it also makes electorates more representative of the overall population. "Comparative studies of turnout note that the relationship between socioeconomic status and voter turnout weakens as turnout increases," Jackman writes, citing this paper. "Thus, to the extent CV [compulsory voting] increases turnout, CV also removes socioeconomic differences in electoral participation. Quite simply, when everyone votes, there can be no socioeconomic 'biases' in turnout."

Eliminating demographic biases could be a huge deal in the US, where voters (especially in midterm elections) tend to be whiter, richer, better educated, and older than the country as a whole is:

The philosophical case for mandatory voting

The Australian experience suggests that compulsory voting disproportionately helps the more left-wing of the two major parties. Studies suggest that Australia's policy has boosted the vote percentage of the left-of-center Australian Labor Party by anywhere from 5 to 7-10 points. But it's unclear if it'd have that effect in the US. Research on non-voters in America suggests that they don't differ too much from voters ideologically. "Analyses of survey data show that no objectively achieved increase in turnout–including compulsory voting–would be a boon to progressive causes or Democratic candidates," political scientists Benjamin Highton of UC - Davis and Raymond Wolfinger of UC - Berkeley conclude. "Simply put, voters differ minimally from all citizens; outcomes would not change if everyone voted."

So mandatory voting wouldn't necessarily benefit one party or another. But it would, by definition, mean that more Americans' views are represented in government, and in particular that minorities and economically vulnerable people would have more of a voice. And both parties should be competing for their vote, rather than being able to ignore their needs. It may be, in the end, that Republicans win that competition — but first it has to be a competition.

The best objection to compulsory voting is that it impinges on peoples' freedom to not vote. But we make citizens perform actions for the collective benefit of society all the time, including everything from objections to mandatory jury duty to taxes to the individual mandate for health insurance. In each of those cases, there's a collective action problem. We want individuals to be on juries or pay taxes or buy health insurance even though doing so would be, from their point of view, irrational. Voting is the same way. Any given voter has very little chance of influencing the election, but if nobody voted the result would be disastrous. So we need people to make choices that might not benefit them personally for the system to work. Traditionally, that's been an argument for mandates. It might be worth considering adding one for voting as well.