21 October 2008

Two sorts of predictions

Lately, there are two things that a lot of people searching for this blog seem to want to know: predictions about the election, and predictions about the World Series.

Baseball Prospectus says the Phillies have a 51.7% chance of winning, and the Rays 48.3%. That seems a bit surprising, though; I would have thought (although I don't like to admit it) that the Rays would be a slight favorite. I suspect there's some difficulty in incorporating the fact that the American League (in which the Rays play) has a higher quality of play that the National League (in which the Phillies play).

And Fivethirtyeight.com says Barack Obama has a 93.8% chance of winning. (The election, not the World Series.) The prediction there is based on a Monte Carlo method which simulates the election results; there's a plot of the number of electoral votes received in the simulations, and it gets spikier and spikier as more and more states become settled one way or the other. (The site's model assumes that states may move between now and Election Day, and as "now" gets closer to Election Day, that effect diminishes.)

What do these two predictions have in common? Fivethirtyeight.com is Nate Silver's web site; he works for Baseball Prospectus.

By the way, various people have said that Fivethirtyeight.com doesn't take into account correlations between states. The most common misconception seems to be that the site assumes the results in each state are independent. This is not true; if you start from the state win probabilities displayed there and combine them under the assumption of independence, you get a distribution much different than the one currently displayed on the site.

3 comments:

Alex said...

Funny. THT uses Jamie Holz as their predictor, and he has the Rays up by a significant margin:

http://www.hardballtimes.com/main/blog_article/world-series-probabilities/

I'm not sure what assumptions Davenport is making in his modeling vs. Holz - it would be very interesting to see.

michaeldcassidy said...

With the evil rotten L.A. out of the way, NOW I root against Phillie. May they get swept.

unapologetic said...

No, michael! If the AL wins, then so does the Republican.