Sampling -- Voluntary Sample

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"Voluntary Samples" are both the worst kind of sample and one of the most common kind of sample. The essence of a voluntary sample is that we do not force items to be in the sample. Certainly, this is generally related to getting samples of people. [We would not have to ask an "M&M" if it wants to be in a sample of "M&M's" where we are looking at the color distribution of those candies!] You have almost certainly been approached to be such a voluntary sample. You get phone calls asking if you will participate in a study by answering a few questions, you get emails asking you to give feedback on items, you are asked to fill out response cards at restaurants and other stores, and so forth. An even more pervasive example of such voluntary sampling is web sites that give you a place to give ratings or reviews. In each case you get to choose if you do or do not want to participate. Such sampling does not represent the general population because it ignores all of the people who do not want to respond to the survey. Furthermore, surveys that are open for people to decide to participate attract participants who tend to have strong feelings about the particular issue. It is easy to create a web site that asks people to answer a few questions about how they view a certain topic. Those people who have strong feelings about that topic will not only vote (and vote often) they will get their like-minded friends to search out and join the survey. However, the possible vast majority of people who have feelings and opinions on the subject but who may not be so rabid will just not participate. As a consequence, any report of the "result" of the survey cannot be assumed to represent anyone but the people who actually responded to the survey.

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©Roger M. Palay     Saline, MI 48176     December, 2015