(Community Matters) This article explains the up to 9pt shift in polling methodology over the last week which is likely to account for a big swing in the polls (on top of the GOP convention bounce
Emory University political scientist Alan Abramowitz is highly skeptical of the new Gallup, USA Today and CBS polls. About the latter, which showed a statistically insignificant two point lead for McCain, Abramowitz said: “One reason for the dramatic difference between the two recent CBS polls is that the two samples differed fairly dramatically in terms of partisan composition. The first sample was 35.2% Democratic, 26.2 percent Republicans, and 38.6 percent independent. The second sample was 34.9% Democratic, 31.1% Republican, and 34.0% independent. That’s a change from a 9 point Democratic advantage to a 3.8 point Democratic advantage. That alone would probably explain about half of the difference in candidate preferences between the two [CBS] polls.” full article here