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October 25, 2004
Analysis of Trends in Major Media Polls
By Alan Abramowitz
It isn't just the tracking polls that seem to be fluttering randomly in the wind. An analysis of polls by six major media outlets (Time, Newsweek, CNN/USA Today/Gallup, CBS/New York Times, Pew, and Fox) that released polls during the first half of October and during the second half of October reveals that there is a strong negative correlation (-.84) between the early October results and the late October results.
In other words, the better Bush was doing relative to Kerry in the early October poll, the worse the was doing in the late October poll. Some of this might be explained by the well known phenomenon of regression toward the mean. If a poll's early October sample had either too many Bush supporters or too few Bush supporters just due to chance, it's late October sample should be closer to the true population mean. But these results went well beyond regression toward the mean. Every poll that was above the overall mean in early October was below the overall mean in late October and every poll that was below the overall mean in in early October was above the overall mean in late October. What this bizarre pattern suggests is that the movements of the major media polls in October, like the movements of the tracking polls, reflect sampling error and peculiarties of the polls rather than real change in the underlying preferences of the electorate.
Posted by Ruy Teixeira at 04:09 PM | link
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