Tuesday, October 19, 2004
So what he's done has taken this 2% break-towards-the-challenger rule (assuming each state has a background level of undecideds of at least 4%), taken every poll that has Bush up by 1% or less, and assumed the undecideds will move that state into Kerry's side of the ledger. I've oversimplified this; Prof. Wang has a more detailed explanation, but I think my oversimplification gets to the logic of his exercise.
It is known to poll analysts that voters who are undecided usually end up voting against the incumbent. In particular, compared with their final poll numbers, incumbents get between 2% less and 1% more. In contrast, challengers do better on average by 3%. These figures are consistent with Cook's estimate that undecideds split at least 75% for the challenger. In today's summary of national polls, the average Bush-Kerry split is 48.5-45.5, which sums to 94%. Assuming 2% for Nader and other candidates, the remaining undecideds are 4%. Splitting these by Cook's rule gives 1% to Bush and 3% to Kerry, reducing the margin by 2%.
Therefore, for the main calculation I will assume that the undecided-voter shift is +2.0% towards Kerry, shift state polls by this amount (using the variable already provided in the script), and proceed with the calculation. Based on state polls in Florida, Ohio and Pennsylvania, I estimate that the proportion of undecided voters in these states is similar to the national figures. Because national polls come more frequently, I will use them to calculate the shift. The size of this shift may change in the final days, and I will be monitoring this.
This new estimate is likely to be more accurate. However, it is also the first change to the calculation that is not neutral, it goes beyond the polling numbers themselves, and it is in a direction that is favorable to my candidate. For example, Florida, Iowa, Ohio and Wisconsin are still toss-ups, but they are now above the 50% probability threshold for Kerry.
Unlike Prof. Wang, the adjustment moves in a direction unfavorable to my candidate, but I think it's an important point nevertheless: Those working towards a Bush victory have to create some reason for undecided voters not to break according to historical trends. Hooting and hollering over the latest polls should be guarded, and the sense of urgency towards getting your own voters out should not in any way diminish. It's kind of like managing against the Yankees -- going to the ninth with a one-run lead in Yankee Stadium may put you right where your opponent wants you. If you've got runners on in the top of the inning, score them.
Hugh may be right that polling in a post-9/11 world is entirely different, but if I'm Karl Rove I'm not moving all-in on that bet.
And if that won't sober you up, read Jim Lindgren.