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Fox is no different from any other propaganda dispensary.
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It comes down to this.
If phone calls are random and this it the partisan mix obtained, then that’s bad.
If phone calls are random, but they have a screen with an intended partisan mix, then it’s good because likely bogus.
But it can get more complicated. They can screen for blacks, graduates, whatever — and generate a partisan mix that way without explicitly trying to load with Dems. That would be good because likely bogus.
As I recall the polls being quoted that are pro Trump screen to a partisan mix that looks like the Gallup sampling of 2014 that is D+5. So screening happens in both directions.