The frustrating thing about Election Day is that no one actually has any information about how it's going until Election Night or later. But thanks to exit polls — conducted immediately after a sample of voters cast their ballots — we can get an early (but not too early) idea of how a race has shaken out before all the votes are counted.

But why do news outlets take so long to release exit poll data? And is it really that reliable? Here's what you need to know about the poll that will shape the way we understand the 2014 midterm elections.

How do exit polls work?

Every November election, exit polls are conducted by a group of media outlets called the National Election Pool: NBC, CBS, ABC, Fox, CNN, and the Associated Press. They hire a pollster to conduct the exit poll, but they're the ones who own the information — and who get to be the first to report the results.

The actual polling is conducted by an army of thousands of interviewers who get sent to hundreds of polling places around the country. Interviewers approach a certain number of voters who are leaving the polling place — the exact fraction surveyed is secret — and ask them to fill out the written exit poll survey.

As early voting has become more popular, it's gotten harder to predict vote totals just by talking to people who vote on Election Day. So in 2008, exit pollsters started conducting pre-election phone polls to ask people if they'd already voted, so they could factor early voters into their projections.

What can you learn from exit polls?

The primary purpose of the exit poll is to allow TV networks and the AP to project who's won races as soon after the polls close as possible. But that's not the only question that the exit poll asks.

Voters are asked to provide basic demographic information like gender, age and ethnicity. Furthermore, they're asked some questions about their personal viewpoints and behaviors — like their religion and churchgoing habits — and questions about major issues facing the country.

That means that the exit poll data is actually more detailed, in some ways, than the official US Census vote tallies that come out several weeks after the election. It can offer the first hints — and often the most important ones — to what voters thought this election was about. That's very important to pundits as they try to interpret what it means.

In 2004, for example, post-election chatter focused on "values voters." Voters who attended religious services regularly had overwhelmingly voted for George W. Bush. That narrative came out of the exit poll data.

Of course, what voters say is important to them is partly what campaigns have told voters is important — there's political science research suggesting that when a campaign hammers particular issues, those are the issues that the candidate's supporters say are most important to them. But the exit poll is still the best opportunity the national media has, in some ways, to figure out who voted, why, and how.

When does the public get to find out about exit poll results?

The media outlets running the exit poll want to be able to describe who's voting, and who they're voting for, to the public as early as possible. But they don't want to have any influence on who ends up voting — they don't want anyone deciding not to vote because they've already seen what the exit polls say, and they don't think their vote will matter. (There's some evidence that this happened back in 1980, when some outlets projected that Ronald Reagan would win the presidential election before polls closed on the West Coast.)

In some countries, like the United Kingdom, it's actually illegal for any media outlet to report exit poll results before the polls close. In the US, it's not illegal, but there's a binding agreement among the media outlets that run the exit poll that none of them is allowed to leak any results before the polls have closed. Since the participating organizations don't want to be locked out of future exit polls, they have every reason not to break that agreement.

Reporters are allowed to see some of the exit poll results as they're being compiled through out the day, but they're under super-strict security — we're talking no-phones-allowed-in-the-room-where-the-results-are-kept levels of security. And there's a strictly regimented schedule for when exit poll results can get released.

Around 5 pm ET, media outlets are allowed to start reporting what the exit poll says about who turned out to vote — the racial, age, or party breakdown of voters. But these are preliminary results, and they're going to be skewed toward people who voted early in the day. So groups who tend to vote later in the day — like young voters — might be underrepresented in the stats that first get announced.

As soon as polls close in a particular state, media outlets are allowed to project who's going to win elections there, based on the exit poll results. In deep-blue or deep-red states, where the outcome of the election isn't really in doubt, media outlets don't waste any time projecting winners. So the minute that 7 pm hits on the East Coast, for example, you can expect to see CNN and the AP make a bunch of projections at once. In states with closer races, media outlets will often wait to get the final exit poll results (including people who voted right before the polls closed), or wait to see how actual vote tallies stack up when precincts start reporting official vote totals.

Don't exit poll results ever get leaked?

There has never been an actual leaked exit poll in the US. But there have been plenty of hoaxes.

If you see anyone on Facebook sharing "LEAKED EXIT POLL RESULTS" while the polls are still open, be very, very skeptical. And definitely don't decide not to vote just because you saw something in a leaked exit poll.

Are exit polls always right?

No. In fact, there are some particular challenges that exit polls have faced for the last several elections, that they still haven't found a way to work out:

Early voters. The phone poll for early voters is a new addition to the exit poll, and it's not clear that the kinks have been worked out yet. It runs into the problems any phone poll has — namely, that it's difficult to poll people who only have mobile phones. Furthermore, the exit pollsters don't typically do early-vote polling in every state; in 2012, only 15 states got early-vote polling.

Small groups. Like any poll, the smaller a sample size is, the less likely it is to be representative. So the exit poll is pretty reliable when it comes to large demographics (men, women, Democrats, Republicans) but gets less reliable when it gets to small demographics (young voters, Jewish voters).

Voters of color. In addition to the general problems with smaller voting demographics, analysts believe that the exit poll has a tendency to oversample a particular kind of voter of color — the kind who lives in majority-white areas.

Here's the logic. Even though the public doesn't know exactly how the exit poll chooses where to go, it's possible to make some educated guesses. The exit poll is trying to predict the margin of victory for one candidate over another across the state. So when it decides which polling places to put interviewers outside of, it's reasonable to assume that it's choosing lots of swing precincts — precincts that are harder to predict and likely to affect the outcome. Those are going to be largely white precincts.

Alternatively, says Matt Barreto of Latino Decisions, exit pollsters might choose a precinct as a benchmark based on the last cycle. For example, if a precinct voted for the Democratic Senator 70 percent to 30 percent in 2008, the pollster might choose to put an exit-poll interviewer at that precinct to see if the Democrat's getting less than 70 percent of the vote this time around. But they're not necessarily paying attention to the racial makeup of those precincts.

Here's why this is a problem: the voters of color pollsters run into in majority-white precincts might not be representative of the voters of color across the state. In particular, according to Latino Decisions, voters of color living among whites are "more assimilated, better educated, higher income, and more conservative than other minority voters."

Check out the difference between the percent of nonwhite voters who had a college degree in 2010, according to the US Census vs. the exit poll:

And the problem's even worse for Latino voters, because exit polls are almost never offered in Spanish — even though over a quarter of Latino voters prefer Spanish to English. So the exit polls oversample English-speaking Latinos.

All of these issues together mean that the exit polls sometimes think that Latino voters are much more favorable to Republicans than they actually are. In 2010, for example, Harry Reid won reelection to the Senate by turning out Latinos to vote against his Republican challenger, Sharron Angle, who was running as a hardcore immigration hawk. But according to the exit polls, 30 percent of Nevada Latinos voted for Angle — many more than voted for John McCain for president in 2008. (When the official vote tallies came out, it became clear that over 90 percent of Latinos had voted for Reid.)

So are exit polls usually biased toward Republicans?

Nope! As a matter of fact, even with the issues listed above, exit polls have historically been biased toward Democrats more often than they've been biased toward Republicans.

In 2004, for example, the exit polls overestimated John Kerry's share of the vote (by "more than one standard error") in 26 states; it overestimated George W. Bush's share in only 4 states. The reason for the error? Bush voters were more likely than Kerry voters to refuse to answer a pollster's questions after they left the voting booth.

How often do exit polls get the outcome wrong ?

Honestly, not that often. The errors in exit polls aren't enough to get the outcome of the race wrong — they just might misstate how much the victor won by, or who supported him/her the most.

So if the polls close on Election Day, and CNN immediately projects that your preferred candidate for Senate is going to lose the election, don't hold your breath for an eventual victory. And don't go around your Election Night party shouting "UNSKEW THE EXIT POLLS!" Because unskewed-polls jokes are so 2012.