Reply #1: EVERYONE needs to read this.

[depakid]

It's very straightforward- and although it presents a little too rosy of a picture, it's good food for thought.

Some excerpts:

You must know who paid for the survey... Polls are not conducted for the good of the world. They are conducted for a reason – either to gain helpful information or to advance a particular cause.
It may be the news organization wants to develop a good story. It may be the politician wants to be re-elected. It may be that the corporation is trying to push sales of its new product. Or a special-interest group may be trying to prove that its views are the views of the entire country.

Most scientific samples use special techniques to be economically feasible. For example, some sampling methods for telephone interviewing do not just pick randomly generated telephone numbers. Only telephone exchanges that are known to contain working residential numbers are selected – to reduce the number of wasted calls. But even a random sample cannot be purely random in practice since some people don't have phones, refuse to answer, or aren't home. (the key question here is whther the non-respondents differ as a group from the respondents- historically, the answer to that question is yes, which has produced embarrassing results like "Dewyey Defeats Truman").

You should always ask if the poll results have been "weighted." This process is usually used to account for unequal probabilities of selection and to adjust slightly the demographics in the sample. You should be aware that a poll could be manipulated unduly by weighting the numbers to produce a desired result. While some weighting may be appropriate, other weighting is not. Weighting a scientific poll is only appropriate to reflect unequal probabilities or to adjust to independent values that are mostly constant.