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A First Look Back

November 3rd, 2004, 10:30am by Sam Wang

In Ohio, many provisional ballots are left to be counted. In the meantime, here is some general analysis. Overall, pre-election polls, exit polls and actual voting are mostly correlated. An exception occurs in Florida, suggesting that something unusual might have happened there, either in voting or in exit and opinion polling. The effect is probably smaller than Bush’s margin.

Voting margins track pre-election polls – with exceptions. Voting margins were more favorable to Bush by 0.9 ±0.6% (median ±SEM; SD, 3.1%) than pre-election polls. This is very near to no difference at all. All discrepancies greater than 5 percentage points (AR, HI, NC, WV) occurred in states with few recent polls. The next largest discrepancy was in Florida, 3.6% towards Bush. Since Florida had so many polls, this is 4 SEM away from zero. Otherwise the match is quite good. Overall, 12 out of 23 pre-election estimates were within 1 SEM of the voting outcome, less than the expected 16 but not bad. I conclude that in most cases this year, five or more likely-voter polls taken in the week before the election gave an estimate that strongly correlated with final voting.

Voting margins and exit polls differ systematically. Exit polls were more favorable to Kerry by 3.0 ± 1.5% (median ±SD) than real voting. This is tentative since I do not have the most complete exit polling data. Currently, in FL I have an exit poll margin of Kerry +1 and a real voting margin of Bush +5%; the discrepancy, 6 points, is again somewhat extreme. This is consistent with the discrepancy noted above. In OH I have an exit poll margin of Kerry +1 and a real voting margin of Bush +2; the discrepancy, 3 points, is right in the middle of the range. I don’t know why exit polls would differ systematically, though one obvious possibility is the gender gap in respondents.

Graphs and further analysis will follow shortly.

Tags: 2004 Election

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