Explained: Margin of error
In mid-October, a Gallup poll of likely voters nationwide showed former Massachusetts Gov. Mitt Romney leading President Barack Obama by a 7 percent margin. That same week, a poll by the University of Connecticut and the Hartford Courant, covering virtually the same time period, showed Obama ahead of Romney by 3 points. That’s a 10-percentage-point disparity.The Gallup poll reported a margin of error of plus or minus 2 percent, while the UConn/Hartford Courant poll reported a 3 percent margin of error — so even if you add the maximum claimed errors, that still leaves a 5-point disparity between the results. As some candidates have observed on the campaign trail, the math just doesn’t seem to add up.But such disparities, in this election season of rapidly shifting tides, have not been all that unusual. So what explains them?There may be several factors at work. For starters, the concept of “margin of...