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Fri Nov 2, 2012, 09:52 PM

Swing State Win Probabilities

It's too late in the season to build a statistical model of the election, but I am interested in doing so. If anyone wants to put together a DU model for use in the next electoral cycle(s) please inbox me. It could be really fun.

But I did write a simple script to calculate probabilities of a win based on the last week of polls for arbitrary states. I assumed normal statistics and simply calculated 1- the probability Obama - Romney was less than zero. I call that the probability we are really ahead as of this moment.

Simple really. Anyhow here are some probabilities we are currently leading in several swing states:

Virginia 83
Ohio 99
Wisconsin 98
Florida 91
Colorado 26
Iowa 94

Interestingly, our probability of being ahead in Ohio is higher than anywhere else. This is in part a consequence of the high polling density that Ohio has experienced.

on edit: sorry, I forget that "normal statistics" isnt' self-explanatory to non-statisticians. Basically I assume that the error in a measurement is distributed according to a bell curve. So mean values are likely to be "close" to the center of the distribution. Large excursions from this value are assumed to fall off, in their probability of occurrence, as the bell curve falls off. Using this curve, it's possible to calculate the probability that the "true mean difference" is actually on the other side of zero (that Romney is really ahead).

Compare the valuefor Florida from a month ago, in the week after the first debate, to see how far we've come. Then there was only a 26% chance that we were in the lead.

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Arrow 4 replies Author Time Post
Reply Swing State Win Probabilities (Original post)
Shivering Jemmy Nov 2012 OP
courseofhistory Nov 2012 #1
Shivering Jemmy Nov 2012 #2
stevend56 Nov 2012 #3
Shivering Jemmy Nov 2012 #4

Response to Shivering Jemmy (Original post)

Fri Nov 2, 2012, 09:55 PM

1. Interesting! Thanks and can

you explain a little how you arrive at these numbers?

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Response to courseofhistory (Reply #1)

Fri Nov 2, 2012, 10:06 PM

2. I put a little more explanation into the body

basically I'm just using MATLAB's ttest function to generate a p-value (probability value) assuming that the data are really random and dsitributed according to a bell curve. Long story short: random fluctuations cannot explain Obama's lead in Ohio.

I edited the post with a somewhat qualitative explanation.


To win, we just have to hope the polls aren't systematically wrong. Hopefully evangelicals are answering their phones as much as anyone else.

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Response to Shivering Jemmy (Original post)

Fri Nov 2, 2012, 10:17 PM

3. Thanks!

Yea, it's been a few decades since I did any probability calculations. But, I could understand your post. We could be looking at another electoral college landslide.

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Response to stevend56 (Reply #3)

Fri Nov 2, 2012, 10:26 PM

4. I'm suspicious of the Florida numbers

it's only just recently swung our way. Throw in polls from earlier, and it goes away, sad to say.

But the only thing keeping me up nights now is that our turnout machine gets cocky and doesn't perform.

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