On April 23, Hillary Clinton, with a net gain of 214,000 Pennsylvania votes in her back pocket, set off an election firestorm by claiming she had slipped ahead of Barack Obama in the popular vote total.

“I’m very proud that as of today, I have received more votes by the people who have voted than anybody else,” she told a rally in Indianapolis.

Journalists immediately fact-checked the statement, pointing out that Clinton’s math relies on counting votes from Florida and Michigan. (Of course, the DNC has stripped those states of their delegates for scheduling their primaries before the party’s calendar allowed, and both Clinton and Obama had agreed to not campaign in either state. Furthermore, in Michigan, Obama asked that his name be removed from the ballot, which naturally kept him from earning a single vote.) Even The New York Times, in a headline, gently called Clinton’s claim “New Math.”

But whether or not Florida and/or Michigan should be counted is only the most obvious pitfall in determining who’s actually winning the popular vote. News audiences—and superdelegates—want to know the popular vote, a simple number that in almost any other election cuts through the intermediation and let’s you know who’s winning. Is that too much to ask?

Well, maybe. The Democratic party’s nominating process is a kaleidoscope of caucuses, conventions, and primaries, sometimes all in the same state. And there’s no obvious best way to estimate a popular vote from it all.

The biggest difference, of course, is between caucuses and primaries. Not only are caucuses low-turnout events (you must be in the room to participate, and they take place in a limited time frame), but four caucus states don’t report the individual caucus-goers’ preferences. Together, those states have a population of more than 11 million, and there is no precise information on how individuals “voted” at those caucuses.

And into this breach steps The Estimate—and a certain amount of disagreement: CNN, MSNBC, The New York Times, and Real Clear Politics all use different strategies to attempt to count these caucus “votes.”

The one thing they all agree on is that, regardless of the strategy, it’s nowhere near an exact science.

“This is an attempt to tally one person, one vote, and to try to get as close to a real number as possible,” says John McIntyre, managing editor of Real Clear Politics, a Web site that’s become a go-to reference for superdelegates, votes, and other election arcana.

“This popular vote thing? The only reason we’ve succumbed to it is that I’ve talked to superdelegates that want to know the total,” says Chuck Todd, NBC’s political director. “But we’ll never get an agreed upon total.”

“We came up with a number. No, not a number, but an estimate,” stresses an off-air member of CNN’s political unit, who was made available on the condition he not be named.

Again, four caucus states—Iowa, Nevada, Maine, and Washington—don’t report raw vote totals. Instead, they report delegate equivalents. These are not the pledged delegates that will be voting at the Democratic convention in Denver. They are low-level delegates—the closest number we have to the raw vote—who will go on to further caucuses at the state, county, or congressional district level; they are the first step toward determining who gets what in Denver. Where the delegate equivalents are selected varies from state to state: in Iowa and Nevada the caucuses take place in every precinct; Maine meets at the town level; and in Washington the first round of caucusing takes place at varying levels of jurisdiction, from whole counties to chopped-up state legislative districts. The delegate equivalents reported from these contests are the only party-sanctioned numbers indicating how strongly a candidate performed.

“These numbers they spit out correlate, to some degree, with how people voted,” says McIntyre.

But exactly how well?

These delegate equivalents are derived from the preferences of individual caucus-goers, or the raw vote. But before becoming delegate equivalents, those votes must essentially first pass through a complicated system of filters that can reflect geography, population, local voting history, and the national party’s requirement that, if possible, any candidate who garners support from more than 15 percent of voters at a caucus site get at least one delegate.

Despite that ambiguity, the delegate equivalents allotted in these four states are the only official numbers out there. As such, they form the basis of most press estimates of the popular vote. How?

Clint Hendler is the managing editor of Mother Jones, and a former deputy editor of CJR.