Regression models are common in social science (Fair's book presents some very good examples), but they sometimes yield implausible results. (See my column on John Lott's "More Guns, Less Crime.") Fair acknowledges that there are particular caveats we should be aware of in evaluating his presidential voting model. One glaring weakness is that there are only 22 data points (6 after the basic model was devised in 1978) with which to fashion the predictive equation.
More generally, we should recognize that a certain degree of data dredging — after-the-fact torturing of data to reveal accidental relationships and meaningless correlations — can always make a model appear more impressive than it is. Rejiggering it so that it "predicts" the past is not particularly difficult.
Furthermore, "voting one's pocketbook" and not "rocking the incumbent's boat" may usually be, but need not always be, the dominant determinants of the vote. 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.
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.
Professor of mathematics at Temple University, John Allen Paulos is the author of best-selling books, including Innumeracy and A Mathematician Plays the Stock Market. His Who’s Counting? column on ABCNEWS.com appears the first weekend of every month.