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augusti 30, 2004

John Allen Paulos om en förutsägelse av det amerikanska valet

I Election Prediction - Four More Years or Four More Variables? beskriver och kritiserar John Allen Paulos en av förutsägelserna av det amerikanska valet.

A well-known Yale economist has written a book using the mathematical technique of regression to predict the outcome of presidential elections. Ray C. Fair's Predicting Presidential Elections and Other Things grew out of his 1978 paper that provides quite accurate descriptions of these quadrennial elections dating back to 1916. Before getting to his very surprising prediction for this November (with which I disagree), let me sketch the idea behind the technique.

Sedan går Paulos Igenom de olika parametrarna som Fair använder för att förutsäga valets utgång, och slutsatsen blir:

The bottom line: the model predicts that the outcome won't even be close. Bush will win somewhere around 58 percent of the vote.

This is quite contrary to the polls and to the election futures markets, both of which indicate a very tight race. Still, before dismissing Fair's prediction out of hand, note that his model has been impressive (in retrospect) over the 22 presidential elections since World War I. Although the model's predictions of the victor were wrong in a couple of very close elections, its predictions of the vote percentages in these years were nevertheless quite accurate.

Men Paulos är kritisk till modellen eftersom den inte tar hänsyn till flera viktiga parametrar:

...
I suspect that other variables — the war in Iraq, cultural and environmental issues, and concerns about civil liberties — will play a more important role in this year's election than in past years, and they are not part of Fair's model. Even the economic factors in his model fail to reflect anxieties over job losses, huge deficits, and increasingly disproportionate inequalities of income.

Han är även principiellt kritiskt till denna typ av regressionsmodeller, vilket även diskuteras. Artikeln avslutas på följande sätt:

The prediction of Fair's model that Bush will win by a wide margin is likely to be disturbing to Kerry supporters and heartening to Bush supporters. Because of the anomalous nature of this election, the testimony of the polls and the election markets, and the frequent unreliability of regression models, however, I do not believe it.

We'll just have to wait until November (or, horrors, December) to see whether Professor Fair's model will be outfitted with new variables and, a bit more importantly, the country outfitted with a new president.

Posted by hakank at augusti 30, 2004 07:39 EM Posted to Statistik/data-analys

Comments

Posted by: Lars Olofsson at augusti 30, 2004 08:34 EM

Posted by: Håkan Kjellerstrand at augusti 30, 2004 08:39 EM