Random variation and US polls
Since 3News has had a story saying that Romney is ahead in the US polls (not up yet, but look here later) I figure it’s worth linking to someone who understands these things, Nate Silver.
In short, yes, a poll by a very respectable group did report Romney as ahead, in a very large swing. But other polls showed much smaller swings. So it’s most likely that part of the result is random variation. It’s true that Romney’s advantage is larger than the margin of error in this poll, but that does happen: one poll in twenty should be outside the margin of error even if there’s nothing more complicated going on.
Nate Silver’s projection including this poll still gives Romney only a 25% chance of winning, about twice what he had before the debate. Intrade‘s betting gives about 35%, up from just over 20%.
[ update: the Princeton Election Consortium meta-analysis of polls has Obama with a 2% lead, down from 6%, but predicted to rise again]
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »