SPRINGFIELD, Ill. (AP) – Like voters in more than 20 other states, Illinoisans are going to the polls and help choose presidential nominees. But the process is more complicated than simply punching the name of a favorite candidate.

Here’s a look at how the Illinois primary works.

Q: What’s at stake in Tuesday’s primary?

A: On the Democratic side, 153 delegates, or 7.5 percent of the total needed to capture the nomination. Of those, 100 are chosen directly by the voters and 53 are appointed by the party based on election results.

Republicans have 57 delegates up for grabs, or 4.8 percent of the total needed.

Both parties also appoint some additional Illinois delegates, most them high-ranking party leaders who can vote as they please.

Q: Is it a “winner take all” election?

A: No. Even losing candidates can pick up some delegates, depending on the results in each congressional district. But the parties use different systems to allocate those delegates.

Q: How do Democrats do it?

A: They use results of presidential voting to decide how many delegates a candidate gets. For instance, if Candidate X gets 60 percent of the statewide vote, then he or she is supposed to get roughly 60 percent of the delegates. It’s not exact because some delegates are chosen by the vote in each congressional district and some are allocated based on statewide results.

Within each district, candidates who get less than 15 percent of the statewide vote are ignored. And the percentages sometimes work out to 4.8 delegates or some other impossible number. When that happens, arcane rules determine how many delegates the candidates get.

Q: How is that different from what Republicans do?

A: The GOP does not use statewide results to choose delegates. In fact, the presidential vote has no bearing whatsoever on which candidate wins the most delegates. It’s purely for show.

Q: Huh?

A: Republican delegates are determined solely by how many votes each delegate — not a presidential candidate — receives in each district. If a district is allotted three delegates, the delegate candidates finishing first, second and third go to the convention, no matter whom they support for president.

Let’s say you support Mike Huckabee for president. If you vote for him at the top of the ticket and then turn in your ballot, you haven’t helped Huckabee win any delegates. To do that, you must go to the delegate section and vote for the people with “Huckabee” beside their name.

Q: Congressional districts all have roughly equal populations, so they all get the same number of delegates, right?

A: Wrong. Delegates aren’t based on population; they’re based on the results of past elections. A district with a lot of Republicans will get more Republican delegates. One with more Democratic voters gets more Democratic delegates. On the GOP side, the number of delegates varies from two to four. For Democrats, it ranges from four to eight.

Q: At the nominating convention, are delegates required to support particular candidates?

A: Generally, yes. While some special delegates can vote however they want, the ones chosen in the primary election must support the candidate to whom they were originally pledged. But if a nominee isn’t chosen on the first ballot, delegates can start switching.

Q: Who are these delegates?

A: Usually, they’re party activists and officeholders — mayors, state lawmakers, business and labor leaders. Since the vote for each delegate matters on the Republican side, GOP presidential candidates often put together slates of well-known local people who will attract votes in their own right. U.S. Rep. Ray LaHood, for instance, is on the ballot as a McCain delegate.