Just how representative are caucus attendees?

Via roguestaffer, here's a new PPP poll (PDF) of likely Democratic primary voters.  Among that group, 40% say they prefer Bennet for the Senate nomination, 34% prefer Romanoff, and 26% remain undecided.  We'll know more tomorrow, but my guess is that the outcome of tonight's precinct caucuses will look almost nothing like that poll.  For one thing, the number of undecided people who will actually participate in the caucuses could probably fit in a Honda Civic.  For another, I'm guessing Romanoff will at least tie.