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notes 9 - Designing Samples Submitted by gfj100 on Tue...

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Designing Samples Submitted by gfj100 on Tue, 11/10/2009 - 16:27 Then entire group of individuals about which information is wanted is called the populations . It ma be somewhat abstract. The part of the population actually examined to gather information is the sample . It is more concrete and immediate than the population. Example Identify the population and the sample in the following: 1. A survey is carried out at a university to estimate the proportion of undergraduates living at home during the current term. Population : all undergraduates at the university; Sample : those undergraduates surveyed. 2. In 2005, investigators chose 400 teachers at random from the National Science Teachers Association list and polled them as to whether or not they believed in biblical creation (hypothetical scenario). 200 hundred of the teachers sampled responded. Population : National Science Teachers Association members; Sample : the 200 respondents. 3. A balanced coin is flipped 500 times and the number of heads is recorded. Population : all coin flips; Sample : the 500 coin flips. Any sample taken should be selected at random; otherwise it may be prone to bias. Bias is the systematic favoring of certain outcomes. For example, people who volunteer for a treatment may bias results toward conclusions that the treatment offers an improvement over a current treatment. A sample should be selected using some probability sampling design which gives each individual or participant a chance of being selected. Four common probability sampling schemes
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