Another article that discusses how the use of polling techniques that over sample one party can change the polls results to reflect conditions that do not exist....The article shows how polling as little as 4 percent more Republicans than Democrats can get the results that occured in the Gallop and CBS polls which showed Bush many points ahead of Kerry. By adjustments to the polls to reflect this oversampling, the Gallop and CBS polls are found to reflect a dead heat...
Divergent Opinion Polls Reflect New Challenges to Tracking Vote
Widely divergent poll results in recent days underscore a paradox of the 2004 presidential race: Despite all the surveys, it may be the toughest election in memory for anyone to track.
Opinion polls themselves had been getting harder to conduct long before the matchup between President George W. Bush and his Democratic rival, Massachusetts Sen. John Kerry. The reasons range from growing reluctance to participate in surveys to increasing reliance on cellphones rather than the land lines pollsters have long used to ensure demographic and geographic balance in surveys...
In the portion of the survey conducted Sept. 8-10, Mr. Bush led Mr. Kerry 52%-40% among registered voters. In a separate portion conducted Sept. 11-14, Messrs. Kerry and Bush were tied at 46%. But there was one other key difference, too: Among voters sampled in the first portion, self-described Republicans outnumbered Democrats by two percentage points; in the second, Democrats outnumbered Republicans by four percentage points...
Yet those CBS surveys were conducted the same way the Pew polls were -- without making any adjustment for the different number of Republicans and Democrats surveyed. And in the CBS polls, the number of Republicans surveyed rose sharply from the first week to the second....
In a close race, in fact, that can make the difference between an apparent dead heat and a solid lead for one candidate. If the CBS and Pew surveys are adjusted to reflect comparable numbers of Republicans and Democrats, their results would have been virtually identical...
http://www.zogby.com/Soundbites/ReadClips.dbm?ID=9493A lot more in this article. It indicates that many other polls, particularly polls that are assigning electoral vote counts are skewed in assigning Electoral votes to Bush because they are relygin on polls that have oversampled Republicans enough to give states to Bush where he has no lead.