This and your post below are very thoughtful for an undergraduate course in statistics – especially the separation of variation and bias – at somepoint it would be nice to hear about how the students dealt with it.

]]>Thanks! That’s a good point about covariance between the states. Indeed, I treated them as independent in computing the Bayes Factor. I do have covariance info from my model because I treat the state-level parameter as the sum of a national parameter and a state-wise deviation, so the swing states tend to have mildly strong positive correlations. I assume that Silver’s model also induces positive correlations, which he doesn’t publish.

]]>I like your blog post!

I think there’s something missing in your analysis: you’re treating the states as independent outcomes. I suspect that Nate includes an uncertainty for nation-wide bias that he could only make explicit by publishing his covariance matrices. Since Nate only posted his diagonal entries, it makes his model look more conservative than it really is.

]]>I gave my results to Andrew a few days ago and he said that they were pretty similar to votamatic’s. I think a lot of those differences are being driven by the non-swing states, for which there is not a lot of polling data (often zero polling data). I just did a blog post comparing my predictions on 538’s on 13 swing states: http://jwrteaching.blogspot.com/2012/11/election-results-fivethirtyeight-and.html

Upshot: both of our predictions are biased toward the Republicans. 538’s standard errors are way too large (all 13 states fall within +/- 1 standard deviation), and I’m killed by the bias.

]]>I’m pretty sure you and your class were overconfident. Here’s a great evaluation comparing (so far) 538 and votamatic performance:

http://www.acthomas.ca/comment/2012/11/538s-uncertainty-estimates-are-as-good-as-they-get.html

Can you send your class’s project to Prof. Thomas to add to his study?

]]>Great idea for a class project

]]>ahem, Intrade, not etrade. http://www.intrade.com/v4/home/

]]>Also, there is an easy way to place monetary bets on election predictions, it’s called etrade. Rumor is, somebody made $20,000 on election day by shorting Romney on etrade.

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