
How (not) to forecast an election: Analysis via a hierarchical Bayesian model - datart
http://datart.com.br/blog/us_2016_elections_en.html
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imh
538 made an interesting point about these kinds of biases. Essentially,
polling errors are correlated. You can't unbias your estimate, but you can
realize that if voters are reluctant to state their Trump preference in
Wisconsin, then they are also likely to be reluctant in Michigan. If you know
how correlated your errors are, you can properly account it in your own
uncertainty, probably leading to a prediction that is closer to 50-50.

~~~
whybroke
Actually the discrepancy stems from underestimating voter turnout for Trump
and over estimating it for Clinton and is not caused by the mythical timid
Trump voter.

~~~
imh
Doesn't matter. All that matters is that the errors are correlated. If voter
turnout is biased in one state, then it likely is in another. The reluctance
was just an example.

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sgt101
"We have found that even a modestly sophisticated statistical model does very
little to counter unreliable data"... so.. garbage in... garbage out?

I have an alternative explanation for this : people who buy newspapers and
mainstream web sites are liberal. Pollsters and analysts who wish to make a
living must get clicks and sell copy. The ones that create models that agree
with the general zeitgeist of the liberal milieu get clicks and sell copy,
other models are gradually ground to extinction.

Markets are not efficient mechanisms for creating insight.

~~~
dandersh
Unfortunately your explanation is not correct. For example, it does not
explain the extensive coverage of Donald Trump that was used to get clicks and
sell copy, despite his violation of everything liberals hold dear...

Early in the campaign, Trump acknowledged his media advantage. “I’ve gotten so
much free advertising, it’s like nothing I’d have expected,” he told the New
York Times in September. “When you look at cable television, a lot of the
programs are 100% Trump, so why would you need more Trump during the
commercial breaks?”[1]

[1][http://www.marketwatch.com/story/trump-has-gotten-
nearly-3-b...](http://www.marketwatch.com/story/trump-has-gotten-
nearly-3-billion-in-free-advertising-2016-05-06)

[http://www.politico.com/blogs/on-media/2016/02/les-
moonves-t...](http://www.politico.com/blogs/on-media/2016/02/les-moonves-
trump-cbs-220001)

~~~
nilkn
The coverage of Trump was entirely negative, though. It makes perfect sense
that one could sell a magazine to liberals by attacking the main competitor to
liberals in the Presidential race.

~~~
dandersh
And the coverage of Hillary wasn't?

~~~
kobeya
The coverage of Hillary tended to criticize her actions (e.g. regarding
emails). The coverage of Trump tended to criticize his character. Objectively
speaking, one was more of an ad hominem attack, which reflects poorly on the
media.

~~~
icebraining
Ad hominem is a fallacy when evaluating an _argument_. When you're evaluating
a person (as a candidate), arguments are necessarily ad hominem, whether
they're about temperament or conduct.

~~~
kobeya
As someone who thinks elections should be decoded by positions on policy not
moral character or temperment, I disagree.

~~~
icebraining
You may disagree with the metric, but that doesn't make it a _fallacy_ , just
a difference of opinion.

~~~
kobeya
I didn't use the word fallacy. You did.

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qwrusz
One of the better articles I've read on why US election forecasts are
inaccurate. And written by a couple of guys from Brazil.

While beyond the scope of this article, it would be great see more research
done into the relative strengths of each bias, i.e. which biases are skewing
polls the most, rather than just using lumped bias terms. Though I did see
after Brexit forecasts got it wrong too the British Polling Council is
"looking into it".

What's most interesting is there wasn't more of an effort by the media to get
accurate vote forecasts before the election. Granted, it's more expensive and
takes longer but it's not terribly difficult to do. It does involve a research
team and statisticians spending time in person in the state and getting deeper
data from people. But the time/costs aren't as outrageous as one would think
because it only needs to be done in the handful of close swing states. And a
sample size of just a few hundred people is enough to get significant results.
Seems obvious and worthwhile, maybe in 2020 they figure it out.

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jonahrd
This is cool! But the bias slider isn't draggable for me on chrome on linux
mint

