Back in the 2008 election, 131 million Americans cast a ballot for president. That's about two-thirds of eligible voters, which seems like a lot. Yet that still left more than 15 million people who were registered but didn't vote. An additional 30 million Americans weren't even registered. Why is that?
Earlier this year, the Census Bureau released an in-depth analysis (pdf) of voters and non-voters in the 2008 election. As Gwen Sharp of Sociological Images pointed out here, the census included a helpful breakdown of reasons that people gave for not voting. Here's why 15 million Americans were registered but didn't vote:
Notice that apathy was a big reason -- roughly 4 million registered voters either weren't interested or didn't like the candidates. But polling place access was a major factor, too. Nearly a million Americans had "registration problems" while 750,000 found the polling location either too inconvenient or had transportation problems. And some 2.6 million voters said they were "too busy" to vote.
Now let's look at the 30 million Americans who weren't registered to vote in the first place in 2008. Their reasons:
Apathy plays a much larger role here -- some 15.5 million Americans didn't register in 2008 because they weren't interested or they outright refused. An additional 1.2 million figured that their vote would not make a difference.
But it wasn't all apathy. Some 5.7 million Americans either didn't know how or where to register or missed the deadlines. An additional 3.6 million Americans weren't eligible to vote, either because they didn't meet residency requirements or for other reasons (four states bar ex-felons from voting, for instance).
Over the years, experts have tried to come up with a number of proposals that might increase turnout. We could make Election Day a national holiday rather than holding it on a Tuesday. We could allow Americans to vote by email. We could make voting mandatory. And so forth. But few of these ideas have caught on yet. As a result, the United States still ranks incredibly low (pdf) among advanced countries in terms of voter turnout.
All in all, the charts above show 45 million American citizens who were either registered but didn't vote or didn't register at all in the last presidential election. According to Census data, that number has gone up steadily with each passing election, so we can likely expect around 50 million people to fall into this category on Tuesday.