Wednesday, January 16, 2008

Michigan Poll Errors

(Darker points are polls taken closer to primary date, lighter points were taken earlier. All polls were completed after the New Hampshire primary.)

The Republican primary polls for Michigan did better than those for New Hampshire, but generally underestimated support for Mitt Romney. Only one poll got both Romney and McCain's vote within the five point error ring.

All three polls completed on January 14th, the day before the primary, got McCain's vote within a small error, but the Romney errors ranged from small to quite large for these last polls. Earlier polling was generally further from the final vote, suggesting that a trend to Romney was partially captured by the late polls, but only imperfectly.

For the second and third place finishers, the polls were quite good for McCain vs. Huckabee, with all three final polls inside the five-ring and all eight polls inside the 10 ring.

The pattern of underestimating the winner's percentage while doing quite well on the 2nd and 3rd place finishers suggests that much of the undecided category in the surveys eventually went to Romney, boosting his total beyond the support registered in the poll, while barely adding to the 2nd and 3rd place totals.