My source for most of my polling data is Real Clear Politics. They do excellent work in collecting polling data and also calculate their own poll averages. For national
polling I currently use their average.

For individual states I do my own calculation based on a
weighted average of polls. Newer polls are given more weight than older polls,
bigger polls are given more weight than smaller polls, and likely voter polls are
given more weight than registered voter polls.

For both national and state polls I estimate a confidence
interval around the number – given what we know is the current poll how far
could the real results actually stray from that poll. In a state with little
polling that could be 5-10 points in either direction, in more heavily polled
states the ranges are narrower. In short, the more polling data I have,
the more confident I am.

This information (what we know about the race in each state,
what we know about the national race) is fed into the model which uses it to
simulate a national election. I repeated the simulation many times, and report
out the aggregate results. Some examples in the 9/13 simulation:

- · President Obama won 84% of the time
- · He won the popular vote in Wisconsin 78% of the time
- · He won the popular vote in Indiana 2% of the time
- · There was an electoral college tie 0.2% of the time
- · 91% of the time, the winner of Michigan was the same as the winner of the election overall.

The simulation is repeated many times because although the
model doesn’t know what will happen, it does know how likely various outcomes
are. Perhaps the right mix of voters will turnout for Romney in OH and FL, or
perhaps a different mix turns out and Obama wins both states. Perhaps something
will happen that swings the election dramatically in Romney’s favor. The model
doesn’t know which will happen, but it can estimate how likely each of these
events are. You have to repeat that simulation many times to capture all the
possible realities and see how they play out together, on average.

If you who are craving a more detailed explanation
(including more detail on confidence intervals, translating voting advantages
into winning percentages, and much more), please see Intro, and National Sim entries.

Seems like this election basically come down to Florida, at least as far as the toss-up states go. How often does either win the election without also winning Florida?

ReplyDeleteGood question - I added flags for win election/lose state (and win/win) to tonight's run. I'm heading to bed but will look through the results more tomorrow.

ReplyDelete