Jay Currie looks at the US election polling:
Polls tend to work by adjusting their samples to reflect demographics and an estimate of a given demographic’s propensity to actually vote. On a toy model basis, you can think of it as a layer cake with each layer representing an age cohort. So, for example, if you look at younger voters 18-29 you might find that 90% of them support Hilly and 10% Trump. If there are 100 of these voters in your sample of 500 a simple projection would suggest 90 votes for Hilly, 10 for Trump. The problem is that it is difficult to know how many of those younger voters will actually go out and vote. As a rule of thumb the older you are the more likely you are to vote so now you have to estimate voting propensity.
There are two ways to get a sense of voting propensity: ask the people in your sample or look at the behaviour of people the same age but in the last couple of elections.
And now the landscape begins to shift. In 2008, nearly 50% of voters aged 18-29 voted. In 2012, 40% voted. In both elections, the youth vote was heavily pro-Obama. If you were designing a poll at this point, what sort of weighting would make sense for youth voters? Making that call will change the landscape your poll will reflect. If you want your poll to tilt Hilly you can believe that the prospect of the first woman President of the United States will be as motivating as Obama was and assign a voting propensity of 40-50%; alternatively, if you don’t see many signs of Hillary catching fire among younger voters, you can set the propensity number at 30% and create a tie or a slight Trump lead.
(The results of this are even more dramatic if you look at the black vote and turnout. In 2008 black turnout was 69.1%, 2012, 67.4% with Obama taking well over 90%. Will the nice white lady achieve anything like these numbers?)
One the other side of the ledger, the turnouts of the less educated have been low for the last two elections. 52% in 2008 and a little less than 50 in 2012. There is room for improvement. Now, as any educated person will tell you, often at length, Trump draws a lot of support in the less educated cohorts. But that support is easily discounted because these people (the deplorables and their ilk) barely show up to vote.
Build your model on the basis that lower education people’s participation in 2016 will be similar to 2008 and 20012 and you will produce a result in line with the 538.com consensus view. But if you think that the tens of thousands people who show up for Trump’s rallies might just show up to vote, you will have a model tending towards the LA Times view of things.
