Are internet polls inflating Donald Trump?

Maybe.  So says Harry Enten:

The problem

Trump has averaged 23.4 percent in live-interview polls since entering the race in mid-June. That’s 5.9 percentage points lower than his standing according to automated phone polls (29.3 percent) and 5.7 percentage points lower than his support in Internet polls (29.1 percent). Here’s the gap since Trump entered the race (to simplify things, I’ve combined automated phone and Internet polls):

enten-datalab-trumplive-1

And the divide isn’t confined to national polls. Trump is also doing better in Iowa and New Hampshire in non-live-interview polls.

My initial thought?  Non-live interview polls are always better at getting people to admit embarrassing information and it is embarrassing to support Trump.  Enten says no:

What about the idea that people don’t want to tell pollsters they support Trump for fear of being thought politically incorrect? Jonathan Robinsonfloated this idea when he first noticed the gap between live-interview and non-live-interview polls. I have a number of problems with this theory.

First, since when are Trump supporters afraid to admit they like Trump? Much of the reason they like Trump in the first place is because he “tells it like it is,” and his supporters often let people know it. Now, all of a sudden, they’re getting shy with pollsters?

Most Trump supporters are not actually the nuts out there attending rallies.  And whether or not they like how Trump tells it like it is, some surely pick up on the fact that being a Trump supporter might not be the most popular thing among your friends and neighbors.  But Enten’s second point is more compellling:

Second, if Trump voters were afraid to admit that they were behind him, we’d expect them to say they were undecided (see the Bradley effect). But, on average, 11.2 percent of voters are undecided in live-interview national Republican primary polls and 7.4 percent in non-live-interview national primary polls. Even if we assigned all these additional undecided Republicans to Trump (which probably isn’t right), this 3.8 percentage point gap doesn’t account for the 5.8 percentage point difference in Trump support between live-interview and non-live-interview surveys.

No, but it does account for a good portion of the gap.  Anyway, I guess we won’t actually know the answer until the voting starts, but it is definitely an interesting question.

About Steve Greene
Professor of Political Science at NC State http://faculty.chass.ncsu.edu/shgreene

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