The median electoral vote (EV) estimate is very sensitive to swings in reported opinion because of the winner-take-all mechanism of awarding EV. Under near-tie conditions I find that the change is about 30 EV per 1-point change in the popular margin. Therefore Kerry’s approximately 110-EV slide since mid-August represents a 4-point swing, equivalent to 2% of voters switching from Kerry to Bush. October 5 and 9 corrections: Looking at the numbers more carefully, from August 1 to mid-September the national popular margin swung by about 8 points, 4% of voters switching. This works out to 12-15 EV gain for one candidate per 1-point change in margin or turnout. For comparison, past EV outcomes were 2000 (Bush) 271-266, 1996 (Clinton) 379-159, 1992 (Clinton) 370-168, 1988 (Bush elder) 426-111-1, 1984 (Reagan) 525-13, 1980 (Reagan) 489-49, 1976 (Carter) 297-240-1. October 9: Historically, the Electoral College margin has shown, on average, a 29 EV margin per 1% popular margin. This is consistent with my calculations this year. Since June, neither Kerry or Bush has gotten much past 320 EV, demonstrating that this is the close race that both campaigns have predicted all along.

In addition to the final polls, the outcome will ultimately be effectively adjusted by three big factors: (a) undecideds, (b) new voter registration, and (c) turnout. Undecideds usually break for the challenger, though this is not certain. Newly registered voters should in principle be reflected in polls, though how many of them pass likely-voter criteria is unclear. Turnout is a big unknown (though a known one). In 2000 Democrats did better than expected from pre-election polls. In 2002, Republicans did better. This year, unusual levels of progressive activism would seem to favor Democrats. But prediction is hard, especially of the future.