« One common type of convenience sample produces surveys that researchers call self-selected opinion polls, or SLOP surveys. As the name suggests, the sample in a SLOP survey is not selected randomly. Instead, individuals choose whether to participate. Margin of sampling error cannot be estimated for a SLOP poll, no matter how large. [...] The people who agree to participate may be different than those who do not.

Researchers have learned, often to their great embarrassment, that these types of samples often produce flawed results. Respondents who volunteer to participate in such surveys tend to be more extreme or otherwise very different in their views than those who do not. In no way can they be said to be representative of the population, so the survey results cannot be used to say anything useful about a target population.

The Internet is awash with SLOP polls that invite people to answer a question and then view the results. In addition to attracting only those with an ax to grind on a particular issue, even the best Internet-derived convenience samples currently tend to include too few older people, minorities and less affluent, less well educated. In short, they tend to miss people who don’t have access to a computer or an Internet connection. These surveys also invite manipulation, as a number of news organizations have learned to their dismay. »

(http://www.aapor.org/badandworsesamples)

Si on ne parle pas des autres questions, est ce parce que les réponses ne correspondent pas aux décisions prises ?

J’aurais bien aimé retrouvé la question sur la nécessité du déficit, juste pour voir comment la question était formulé…