Over at The Monkey Cage, John Sides has a quick post following up on my Q & A with him about the predictive value — or lack thereof — of early polling.

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.

If you'd like to get email from CJR writers and editors, add your email address to our newsletter roll and we'll be in touch.

Greg Marx is an adjunct lecturer at The Medill School and a facilitator with The OpEd Project. She served as an editorial board member, columnist, library director, and No. 2 in the features department of the Chicago Sun-Times.