Today is National Voter Registration Day, and many civic groups — and celebrities like singer Janelle Monáe — are encouraging citizens to make sure they are registered. Election reform and voting rights advocates are also using the event to point to needed changes in the country's registration system to ensure citizens have unfettered access to the ballot box.

The scale of the problems facing the nation's voter registration systems are well-known. The bipartisan Presidential Commission on Election Administration in 2013 concluded that "as many as eight percent of registration records (representing 16 million people) are invalid or significantly inaccurate." A Federal Election Commission report discovered that more than 3.6 million people experienced registration problems in 2012.

How to fix the country's voter registration problems? There is a wealth of evidence for reforms that can help ensure more citizens are able to take the important first step of getting on the voter rolls:

1) SAME-DAY/ELECTION DAY REGISTRATION: Earlier this year, election expert Tova Wang of the policy group Demos surveyed the research [pdf] behind various election reforms. Among the measures with the most data attesting to effectiveness was same-day or Election Day registration. Twelve states currently have some form of same-day registration, although none are in the South. North Carolina's experiment with same-day registration during early voting was one of the casualties of a sweeping 2013 state law (now mired in litigation) passed by conservative lawmakers.*

2) AGENCY REGISTRATION: The National Voter Registration Act of 1993, which mandated that motor vehicle and public assistance agencies offer voter registration, has been a big success: The U.S. Election Assistance Commission found [pdf] that in 2011-2012, 20.3 million voter applications — by far the single biggest sources of voter registrations — came through state offices that issue driver's licenses. Another 2 million people submitted registration forms at public assistance agencies.

But the success of the law also hinges on its implementation. Another 2015 Demos study found wide variance in how states were using "motor voter" and agency registration, with Alabama and Mississippi ranking at the bottom in terms of number of DMV transactions that included a voter registration. In North Carolina, voting advocates noted earlier this year that agency registrations declined sharply under the administration of Gov. Pat McCrory (R), who also brought in a new state election chief.

3) ONLINE REGISTRATION: Pioneered in Arizona in 2002, online registration was offered by 23 states as of last month, according to the National Conference on State Legislatures. Another five states plus the District of Columbia had passed legislation for online registration systems but hadn't implemented them. So far, Georgia, Louisiana, South Carolina and Virginia were the only states in the South to offer the reform, which case studies have shown have increased voter convenience as well as saved states money.

4) AUTOMATIC REGISTRATION: In March 2015, Oregon became the first state in the country to automatically register voters who have driver's licenses (and don't choose to opt out of being registered) — a move which is expected to add 300,000 voters to the rolls by 2016. Although the idea has been floated since the mid-1970s, when President Carter proposed automatic registration, it was considered a non-starter. But since the law passed in Oregon momentum has grown: According to the Brennan Center, legislators in 17 states and the District of Columbia introduced various versions of automatic registration (with California and New Jersey passing it), and Democratic presidential candidates Hillary Clinton and Bernie Sanders have made it a centerpiece of their policy platforms.

5) ENFRANCHISING CITIZENS WITH PAST FELONY CONVICTIONS: A large share of the nearly 6 million people nationally who are barred from voting due to past felony convictions live in the South. Felony disenfranchisement laws have a unique history in the South, where they were often used as a tool to limit the political power of African Americans. In 2012, according to an Institute for Southern Studies analysis, 70 percent of those disenfranchised were in Southern states. Nationally, the Washington, D.C.-based Sentencing Project estimates these laws currently prevent nearly one out of 13 otherwise eligible African-American citizens from being able to vote.

There are other measures that advocates say can help boost registration numbers. Modernizing registration technology, increasing registration portability between states, and allowing teenagers to pre-register before their 18th birthday have all been used successfully by various states.

Of course, making sure citizens are registered to vote is no guarantee they will actually cast a ballot. Getting voters to the polls hinges on other critical factors, including the quality of candidates, the ability of groups and interests to mobilize voters and other elements that influence turnout. But, as Ari Berman argues this week in The Nation, registration is a key first step:

During the 2012 election, the United States ranked 31st of 34 developed countries in voter turnout. Yet 84 percent of registered voters cast ballots. The US doesn't have a voter turnout problem; we have a voter registration problem. Our turnout is abysmal because so many eligible voters are not even registered to vote.

* NOTE: As a result of an injunction granted in the wake of the lawsuit brought by North Carolina voters against the state's 2013 voting law, same-day registration during early voting, as well as out-of-precinct voting during Election Day, have been at least temporarily restored in N.C. That means that, barring any further decision by federal district judge Thomas D. Schroeder, they will be in effect for local elections in the state in 2015 -- although many pages on the N.C. State Board of Elections website as of this writing still claim North Carolina requires a 25-day waiting period to register.