None of the major polls weights by party ID. They weight by demographics. For example, if there are not enough blacks and latinos in their sample, they will overweight their black and latino responses. If there are not enough young people, they will overweight their young voter responses. This often results in a weighting towards Democrats, but it is not weighted to meet a particular party ID split, only to meet a particular demographic split.
You can see this in the numbers that nonniey posted a while back in this thread: http://www.quinnipiac.edu/institutes...ReleaseID=1812
The Florida sample was heavily weighted towards Democrats because minorities were undersampled, as shown in this word document: http://www.quinnipiac.edu/images/pol...2012_demos.doc
But in Virginia and Ohio, the weighted party breakdown closely matches the actual sample because the polls reached a representative number of minorities.



-TJ 
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