Stephen A. Lawrence wrote:
> Oh, I don't know -- keep in mind that the "random" sample is actually > self selected. Have you ever consented to answer a phone survey? It isn't supposed to be self-selected. There are ways to reduce that bias. Granted, the methods are not perfect. Does it say these are telephone interviews? Fully self-selected samples are, for example, when you set up a questionnaire on a web site. Fully non-self selected is the U.S. Census, now underway. There are gradations in between. The commercial phone surveys about radio stations with few respondents probably are toward the self-selected side. The telephone polls before political elections are remarkably accurate these days, despite problems with cell phone. Of course, people who vote in an election are self selecting by definition, aren't they? If you are likely to tell someone on the phone what you think, you are also likely to vote, I suppose. Voters are self-selected except in Australia, where it is against the law not to vote. - Jed
