I've long been suspicious of polls, especially political polls. I also dislike polls because they turn elections into horse races rather than thoughtful consideration of candidates and because they reinforce the myth of "the two-party system".
The first question is who is asking what questions of who.
Who are the pollsters? Are they completely neutral or are they hired by a party or a candidate?
What are the questions and what order were they made? Were the questions framed to get a desired response? Were questions asked in an order to set up the responder for a desired answer?
Who responded to the poll? Was it only people who happened to be at home? Was it only people who always answer the phone and politely enter into a dialog? How many people screen their calls and won't respond to pollsters or other solicitation calls? How many people who did answer hung up right away? What about people who only have cell phones? Even if cell phones are called by pollsters, do the phone owners screen their calls and don't respond to unknown callers?
For some of these difficulties facing pollsters, see "Pollsters struggle to find the right sample of voters", John Harwood, Star Tribune, 2012-08-06.
Polls also can be very far off. One iconic picture is Harry Truman holding up a newspaper in November 1948, "Dewey Wins". Harry Truman didn't even stay up for the results, but the polls were way off. It was one of the first telephone polls, but nobody seemed to think that many Democratic voters didn't have telephones.
More recently, the 1998 Minnesota gubernatorial polls predicted Hubert Humphrey III (DFL), Norm Coleman (Rep), and Jesse Ventura (Reform Party) in that order. The result was just the opposite with Ventura winning with 36.99 percent of the votes. The turnout was 60 percent, and so Ventura came in second to none of the above. See http://en.wikipedia.org/wiki/Minnesota_gubernatorial_election,_1998.
I wonder if anyone bothered taking a poll of the 40 percent who didn't show up. What fraction were Democrats who didn't feel Humphrey would do "enough", what fraction were ex-Republicans who didn't like the direction the party was taking even then, and what fraction were people who just didn't give a damn about getting good governance?
