I never knew this. Via an op-ed in today's NYT:
An early order of business in each Democratic precinct caucus in Iowa is a count of the candidate preferences of the attendees. For all practical purposes, this is just what the polls try to measure. But Iowa Democrats keep the data hidden. The one-person, one-vote results from each caucus are snail-mailed to party headquarters and placed in a database, never disclosed to the press or made available for inspection.
Instead, the Democratic Party releases the percentage of “delegate equivalents” won by each candidate. The percentage broadcast on the networks and reported in the newspapers is the candidate’s share of the 2,500 delegates the party apportions across Iowa’s 99 counties, based on Democratic voter turnout in each of the 1,784 precincts in the two most recent general elections. So, the turnout for a candidate in a precinct caucus could be huge, yet the candidate’s share of the delegate pie could be quite small — if that precinct had low voter turnout in 2004 and 2006.
Under the formulas used to apportion delegates, it is possible that the candidate with the highest percentage of delegate equivalents — that is, the headline “winner” — did not really lead in the “popular vote” at the caucuses.
http://www.nytimes.com/2007/12/18/opinion/18cranberg.html?_r=1&ref=opinion&oref=slogin