Sides passes on the following graph from the researchers Chris Wlezien and Robert Erikson, which tracks the predictive ability of presidential polls from 300 days before a general election right up to the vote. In the figure, which covers the period 1956-2008, a higher r-squared number means a poll had greater predictive value:
Unsurprisingly, polls generally become better predictors as the election comes nearer. But beyond that, Sides notes:
The graph shows that polls 300 days [before the vote] have little predictive value at all. The r-squared values increase sharply during the next 3 months or so—when the eventual nominees are becoming better known during the primaries—and then increase more sharply again in the 3 months before the election, when the general election campaign is underway.
For those keeping score at home, there are now 530 days until Election Day 2012.Greg Marx is an associate editor at CJR. Follow him on Twitter @gregamarx.