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Sunday, November 6, 2016

Voters Aren't Changing Their Minds, Only Their Enthusiasm

If you've been curious as to why some polls, like ABC news, have shown significant swings while others, like IBD/TIPP, have been steady it's not because "polls suck" or because of voters changing their minds in the final days. Most of the variation comes down to how pollsters determine the universe of likely voters.
Whereas support for one candidate over the other hasn't been shifting, the intensity of support has been changing. As intensity falls for a candidate some voters fall out of the likely voter model. ABC News has a model that is far more sensitive to those changes than is the IBD (and some other) models. After the FBI news, ABC noted a drop in Clinton enthusiasm and a rise in Trump enthusiasm- so their poll closed. Enthusiasm for Clinton is now recovering, so she has regained the lead. IBD has been less sensitive to changes in likely voters so their poll has shown a more steady race.
Now ABC News has Clinton up 5 and IBD has Trump up 1 point. These polls don't disagree. Because polls are just samples they have error margins - usually in the neighborhood of 3.5-5 points. So +5 and -1 are not incompatible. The closer a poll result is to 50/50 the harder it is to determine who is actually ahead. As you move away from 50/50 the probability that the person on the lead is actually in the lead grows. So in a poll where a candidate is ahead by 3 there is a greater probability that the person is actually ahead than with a poll showing a 1 point lead.
So RealClearPolitics shows Clinton with an average lead of 2 points - but Trump is up in only 1 poll and tied in another. And there are polls with Clinton up 3, 4, or 5 points. This means there is a greater probability that Clinton is ahead.
In the final 3 days of the election I'll be looking for any trend shifts. We should see some new polls today and tomorrow. In 2012 the final few polls showed a clear movement toward Obama and he wound up winning by a margin that doubled his poll average - and it pulled the close states like Florida along with him. If this race stays flat at its current level then Clinton wins with a narrow Electoral College victory. If things shift toward her then she likely claims close states like FL, NC and maybe OH and wins with well over 300 electoral votes. If things *shift* to Trump - then it's anyone's guess.

*with apologies to my Mom for missing the "f" in shift in my initial post...