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About the Murphy Trend in NY-20

Topics: NY-20 , Siena Institute

The final poll (release, crosstabs) by the non-partisan Siena Institute certainly gives Democrats reasons to be optimistic: The trend is all Murphy, with the Democrat improving his performance on each successive poll and now holding a slight (though not yet statistically significant) four-point lead (47% to 43%). The trend is consistent with earlier internal polls conducted by the two campaigns. If we focus only on the trend, it is hard not to consider Murphy a slight favorite, especially since the final Siena poll came out of the field with four days left until voting begins on Tuesday.

2009-03-27_NY20.png

However, we also see three reasons for caution about these results:

  • The margin on the final Siena survey is still within the margin of error, which is to say we cannot be at least 95% confident that Murphy is leading. That does NOT mean the survey amounts to a "statistical tie." If this final snapshot were a perfect random sample of truly likely voters (a very big and essentially impossible "if" for any pre-election poll), we could be roughly 80% confident that Murphy really leads.
  • Predicting turnout in this sort of special election-- and thus selecting "likely voters -- is far more difficult than in a November general election. So there is more room than usual for the possibility that all of these surveys are measuring the wrong likely electorate.
  • Finally, as of this final Siena poll, Murphy has closed virtually all of Tedisco's early advantage in name recognition. Eight-six (86%) can now rate Murphy compared to 89% that can rate Tedisco, the the Democrat may have little room to grow over the last few days of the campaign.
Update: The Hill gets pushback on the poll from the Tedisco campaign and misinterprets the poll's 3.2 % margin of error (via Chris Good).  Remember, the margin of error applies to each percentage separately (i.e. 47% +/- 3% and 43% +/- 3%), not to the difference between the percentages.  

 

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