JimBowie1958
Old Fogey
- Sep 25, 2011
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Incumbent Rule
These polls that show large undecided vote and the President at less than 50% are bad news for Obama. If the poll shows 47% Obama and 45% Romney, that means Romney picks up 6% of the undecideds for the 51% win.
The fact that challengers received a majority of the undecided vote in 82% of the cases studied proves that undecideds do not split proportionally. If there were a tendency for them to split proportionally we would see most undecided voters moving to incumbents, since incumbents win most elections. Similarly, even accounting for sample error, its clear from the chart above that undecideds do not split equally.
For poll users and reporters this phenomenon, which we call the Incumbent Rule, means:
Incumbent races should not be characterized in terms of point spread. If a poll shows one candidate leading 50% to 40%, with 10% undecided, a 10-point spread will occur on election day only if undecideds split equally (i.e. a 55% to 45% outcome). Since most of the 10 points in the undecided category are likely to go to the challenger, polls are a lot closer than they look 50% to 40% is likely to become 52% to 48%, on election day. If a poll is a mirror of public opinion, think of an incumbent poll as one in which objects are closer than they appear.
An incumbent leading with less than 50% (against one challenger) is frequently in trouble; how much depends on how much less than 50%. A common pattern has been for incumbents ahead with 50% or less to end up losing. Final polls showing losing incumbents ahead are accurate. The important question is whether results are reported with an understanding of how undecideds decide.
Many polls may have been improperly analyzed and reported. Some postmortem accounts of polls have been inaccurate -- many polls remembered as wrong were, in fact, right. Its only natural to interpret the term "undecided" literally. But as with so many other findings in survey research, data should be analyzed according to what they mean, not what they say.
These polls that show large undecided vote and the President at less than 50% are bad news for Obama. If the poll shows 47% Obama and 45% Romney, that means Romney picks up 6% of the undecideds for the 51% win.