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Old 11-04-2012, 06:01 PM   #1
GameTheory
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Join Date: Dec 2001
Posts: 6,128
Nate Silver can suck it

I kid Nate Silver, I kid.

Ok, let's talk about polls while we still have a chance! Yeah! I'm starting a new thread here to give the prez odds thread a break, and also to draw more attention to myself.

As a jumping off point, let's look at some things wonderboy Nate Silver has to say in his explanation/defense of his model:

http://fivethirtyeight.blogs.nytimes...-the-favorite/

In reaction to some "pushback" against his projection as Obama as a solid favorite, he responds:
Quote:
What I find confounding about this is that the argument we’re making is exceedingly simple. Here it is:

Obama’s ahead in Ohio.

A somewhat-more-complicated version:

Mr. Obama is leading in the polls of Ohio and other states that would suffice for him to win 270 electoral votes, and by a margin that has historically translated into victory a fairly high percentage of the time.

The argument that Mr. Obama isn’t the favorite is the one that requires more finesse. If you take the polls at face value, then the popular vote might be a tossup, but the Electoral College favors Mr. Obama.

So you have to make some case for why the polls shouldn’t be taken at face value.
So far, so good. And he's right, you do need to justify yourself if you are not going to take the polls at face value. But he's missing half of that equation. You also have to justify yourself if you ARE going to take the polls at face value. What I'm going to argue is that there is no "face value" to a poll. The impression is that a poll is what it is ("it's scientific!"), and if you are going to tweak it, then you better have a good reason. That's true, but again you also need a good reason to accept it as-is since they are tweaked by the pollster and we need to know their reasons in order to accept them. Or maybe they are not tweaked by the pollster and they let the chips fall where they may, but I will argue that that is a distinction without a difference. (I think they SHOULD tweak the samples generally because it is necessary to correct for sampling errors.)

So then Nate goes on to say that it is possible that most of the polls could be biased in one direction. He expands on this in the next day's post:

http://fivethirtyeight.blogs.nytimes...ically-biased/

I recommend you read both of those if you are interested, but the newer post can be summed up by it's title: "For Romney to win state polls must be statistically biased". And that's absolutely true, so an even shorter summary might be "Duh." And his main argument against them not being biased is recent history of them being more-or-less correct. He does claim, by the way, that his model explicitly accounts for this possible bias (whether it is for or against a particular candidate). From the second article:
Quote:
The FiveThirtyEight forecast accounts for this possibility. Its estimates of the uncertainty in the race are based on how accurate the polls have been under real-world conditions since 1968, and not the idealized assumption that random sampling error alone accounts for entire reason for doubt.
It is unclear what his actual method is here -- it sounds like he is not really talking about adjusting the accuracy of individual polls (I don't think), but adding a measure of uncertainty to his simulations that creation his projections. I think he does some sort of Monte Carlo simulation, but I haven't followed him enough to know. Anyway, from what I've read of him (which is fairly lightly) I gather he does not dig into individual polls and simply creates his weighted average without considering the poll internals. But really I'm not sure -- certainly he doesn't seem to talk about adjusting polls individually, and I've seen him be dismissive of the idea of digging into individual polls because he doesn't weight any one poll very much and seems to assume that bias errors will generally cancel themselves out in the average. (I've got his book sitting here -- if he turns out to be right about everything maybe I'll read it.) But in this latest article he is acknowledging the idea that most of the polls could in fact be tilted in one direction which would bias his projection also, but since he doesn't really believe it he isn't going into depth on the ways he could be wrong. So let's cover some of that ground. But despite the title (which is mainly for forum user "Jake"'s benefit), this post actually isn't about Nate Silver other than a starting point indicating what the general consensus on the polls out in the world is, or at least in liberal circles. Anyway, let's now leave Mr. Silver aside.

(cont...)
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