I am frequently asked what the “surprise elections” will be this fall. After all, there are always a few races whose outcome—or near outcome, the results much closer than expected—seem to come out of the blue. …
The surprise outcome in November 2016 was the disparity between the state-level polls and expected outcomes—specifically in Wisconsin, Pennsylvania, and Michigan — and, therefore, the Electoral College outcome. …
The point of rehashing all of this is that public polling on the state level is considerably more problematic than on the national level, even in presidential years with higher voter turnout. In midterm elections, with a third fewer people voting, state and local polls are even less dependable—hence caution should be exercised in putting too much confidence in them. Some are conducted by reputable organizations with usually strong records, others by fly-by-night outfits releasing polls just for their PR value. That means even the poll averages should be approached with some degree of skepticism. CONT.
Charlie Cook