Friday, January 04, 2008

Iowa 2008 Trend, Entrance Poll and Outcome

Last week I took a look at how the poll trend estimates did in the 2004 Iowa Democratic Caucus. This morning we have two new data points for comparison.

It has been a long day and night, so I won't say much tonight. We will look at the polls in more detail after a bit of sleep.

The bottom line in 2004 was that the polls under-estimated winners and over-estimated losers. (See the plot below for the 2004 comparison.) This year again the poll trend substantially underestimated the size of Obama's win. Clinton was quite well estimated, and Edwards did significantly better than the poll trend estimated.

The complex reallocation of preferences in the Democratic caucus also affected the entrance poll, which was quite close for Obama and Clinton but underestimated Edwards' final share of delegates.

The lower tier of candidates all finished below their poll trend estimates, though at such low levels of support that none of the errors are large.

On the Republican side, with a simpler form of voting at the caucus, the polls did a bit better, except again for substantially underestimating the winner, Mike Huckabee. Other candidates ended up with shares of the caucus vote pretty close to their poll trend estimates. Ron Paul did a little better than the poll trend and Giuliani a little worse.