

Nate Silver vs. The Betting Markets - davidmathers

For the record, on the night before the election:<p>(Obama is first number, McCain second)<p>fivethirtyeight.com:<p><pre><code>  OH: 86% - 14%
  FL: 67% - 33%
  NC: 59% - 41%
  MO: 47% - 53%
  IN: 36% - 64%
  ND: 34% - 66%
  MT: 23% - 77%
</code></pre>
intrade.com:<p><pre><code>  OH: 75% - 24%
  FL: 77% - 25%
  NC: 65% - 43%
  MO: 52% - 50%
  IN: 39% - 67%
  ND: 27% - 76%
  MT: 33% - 78%
</code></pre>
betfair.com:<p><pre><code>  OH: 80% - 18%
  FL: 78% - 24%
  NC: 61% - 40%
  MO: 53% - 51%
  IN: 41% - 65%
  ND: 31% - 73%
  MT: 30% - 72%
</code></pre>
Final Scores:<p>Nate Silver (McCain gets MO): Obama 353, McCain 185<p>Betting Markets (Obama gets MO): Obama 364, McCain 174<p>Karl Rove (McCain gets MO and NC): Obama 338, McCain 200<p>pollster.com (McCain MO, NC, FL): Obama 311, McCain 227
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robg
The likelihood numbers cannot be tested empirically. The experiment only gets
run once. In other words, there is no error term for the likelihood numbers.

I'll be looking at Electoral Votes and the popular margin. There the
difference between pollster and 538 is the most interesting to me. The former
is a simple average of all polls while the latter uses weighted averages.
Individual pollsters might get closer but within their margins of error.

~~~
jedc
But the markets (and fivethirtyeight projections) exist for every state.
Together they're a decent dataset, though still a bit light.

I, too, am very interested in comparing betting (prediction) markets versus
poll-based probabilistic forecasts. I wrote more about this here:

[http://blog.mercury-rac.com/2008/11/03/election-tuesday-
what...](http://blog.mercury-rac.com/2008/11/03/election-tuesday-what-to-
expect-from-the-prediction-markets/)

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ca98am79
So far the actual results are:

OH: Obama

FL: Obama

NC: ?

MO: ?

IN: Obama

ND: McCain

MT: McCain

All were wrong with IN.

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jpavlik
Silver also said the Tampa Bay Rays would win 88 games, and people thought he
was nuts. They won 97.

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jyothi
I think the bradley effect would happen again and McCain might get a surprise
win.

It is indeed astonishing that no over is McCain a favorite to bet on.

~~~
robg
Conversely, there's the cellphone effect:

[http://www.fivethirtyeight.com/2008/11/cellphone-effect-
cont...](http://www.fivethirtyeight.com/2008/11/cellphone-effect-
continued.html)

~~~
dejb
True. Both effects might true. However the 2 don't cancel each other out
probabilitisticly. Given that McCain is so far behind the mere possibility of
a Bradley effect favours him. Let's say both effects are 50% likely to exist
and would sway votes by enough to tip the election. Then the results would be

25% Bradley + No Cellphone = McCain wins 50% Bradley + Cellphone = Obama wins
25% No Bradley + Callphone = Obama wins

So in this example McCain now has a 25% chance. Of course this is an
exagerated example but hopefully you get the point.

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johnyymathew
nice article!!! \------------ johnyymathew <a
href="<http://www.bettingchoice.co.uk/>" rel="dofollow">online football
betting tips, odds, news</a>

------
patrickg-zill
Nate Silver is conducting a propaganda campaign on behalf of Obama. He is not
even close to being an honest pollster.

See <http://seanmalstrom.wordpress.com/> (long post, search for "silver" in
the text)

~~~
jonknee
He has been open with his support for Obama. But he's a numbers guy, I don't
see where his math is biased. Likewise, he's a Cubs fan but his baseball
research isn't slanted towards the Cubbies.

Your link just says because Nate Silver talks about Obama in his blog the site
is a propaganda tool. People don't visit for the blog, they visit for the
numbers and research. Personally I think it would be the other way around, if
he were also a popular Obama blogger but did FiveThirtyEight anonymously that
could be considered sinister (it still wouldn't be unless the model was proven
wrong, but there would be a perception of deception).

I've seen him a couple times on HDNET and he's extremely clever. I'll be
watching him tonight instead of the hacks they put up on the major networks.

~~~
gamble
I find it informative to compare Silver's projections with the Real Clear
Politics averages. RCP is a group project, but it's pretty clear that their
editorial views skew heavily toward the conservative end of the spectrum.
Assuming either is biased, I figure that Obama can't be doing any worse than
RCP is projecting or much better than FiveThirtyEight.

