Monday, January 21, 2008

South Carolina and Nevada Poll Errors

Polling for the South Carolina Republican primary mostly got the winner right, but large undecided percentages prior to the election accounted for a general underestimate of the final vote for both McCain and Huckabee. Late polling also found the race closer than the eventual outcome.

Pollng for third and fourth place was less successful in detecting Fred Thompson's final strength and the drop of support for Mitt Romney, who abandoned South Carolina to spend time in Nevada, where he scored a strong first place finish. While almost all the polls finished inside the "5-ring", correctly seeing a close fight for the 3-4 spots, all but one poll got the order of Thompson-Romney wrong (and the one that got that order right substantially missed the magnitude of both votes.)

In the Nevada Republican caucuses the polls wildly underestimated Romney's final strength of 51% of the vote. (Note that the rings here have to be rescaled to include the very large errors.) Even the best of the three Nevada polls was more that 15 points off on Romney. The earliest of the three polls, taken before Romney's win in Michigan, was over 30 points low.

McCain and Huckabee ignored Nevada, essentially conceding the state to Romney, but the polling still failed to pick up the magnitude of his support there.

The polling likewise failed to capture Ron Paul's second place strength. Preelection polls put Paul at about 7% compared to his finish of 13.7%.

In terms of erroneous expectations, the polling also put McCain well ahead of Paul, uniformly getting the 2nd and 3rd place finishers wrong.

On the Democratic side, the final poll was inside the "10-ring", and the polling improved as the caucus approached. Here the surprisingly poor showing of John Edwards, and the Democrat's caucus reallocation rules for non-viable candidates helped boost the final percentages away from the polls. The three most recent polls all got the order of finish correct.