![]() ![]() For example, people who work unusual hours or who travel a lot may be selected to be included in the sample, but are not available when you attempt to contact them. Some of the problems associated with using the telephone book are it excludes those who do not have a telephone, those who have unlisted numbers, and more recently relevant, those who use a cell phone instead of a land line for all their calls.Ī second barrier to purely random samples is for some people in the population, you will find it difficult or impossible to locate them. Many times, the telephone book for a city is used. One of the most difficult steps is obtaining a complete list of every member in the population you want to sample from. In the real world, a truly random sample is difficult to achieve, but you can come close. If a sampler does not use random selection, the sample will favor selection of certain groups, possibly without the sampler even realizing it. Random selection allows impersonal choice to choose the sample, rather than the individual performing the poll (the sampler) to select their own participants or self-selection of respondents as in the voluntary response poll mentioned above. Randomly selecting the members of a sample is important because it helps prevent bias in your results. ![]() Therefore, the sample results are biased and not representative of the population the magazine is making a conclusion about (Americans). These are very specific groups of people that have characteristics that may not be representative of the United States population as a whole. Think of readers of “Fish and Game” or “Science.” Do you think they have different proportions of male and female readers than the United States population? Do you think they are more or less likely to live in urban or rural areas than the proportions in the United States population? They tend to have proportionally more male readers and more readers that live in rural areas. Readers of “Fish and Game” or “Science" are not representative of the entire U.S. A unit might be a person, animal, plant, school, company or other object. A unit is a single member in a nite population we wish to study. The rst is a random sample from a nite population of units. ![]() Second, this sample is not representative of Americans because this sample is based on a group of people that are similar in a particular way (common interest in reading the magazine). Random sampling has subtle aspects when considered formally.First, this type of survey requires the voluntary response of the readers those that feel strongly about an issue will voluntarily respond more frequently than those who do not, resulting in very biased results.There are a couple of reasons why polls of this sort are NOT RELIABLE: “In our last issue, we asked readers to respond to the following question: ‘Do you think your mechanic is honest?’ Based on this poll of our readers, 79% of Americans do not trust their car mechanic.” It is common to read magazine polls that go something like this: ![]()
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