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Determining sample size when planning statistical study

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Determining sample-size is important step when planning a statistical study. It is also quite a difficult task since many variables must be considered.

In Yahoo! use the search term "Sample Size Determination." Select a University or Government webpage that discusses the topic. Do not use Wikipedia, eHow or about.com or other resource that is not written or published by a University or the US Government.

Paragraph 1: In simple terms explain what researchers must go through to select the right sample size for a study. (Be sure to cite and reference the website)
In Yahoo! use the search term "Sample Size Calculator." Select two calculators you like best.

Paragraph 2: Explain how the calculators work. Test the two calculators using a population, confidence level and confidence interval you select. Discuss the results. (Be sure to cite and reference the website)

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The expert determines the sample size when planning statistical studies.

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1. Selecting the correct sample size can be a difficult and time-consuming process. There are many factors to consider when choosing a suitable sample size. The sample size must be large enough as to have a significant magnitude, that is, there must be a sample size that is sufficient enough to be statistically significant (Lenth 2001). At the same time, the sample size must not be too large as to be a waste of resources (Lenth 2001). When determining the appropriate sample size, one must consider the desired width of the confidence interval and whether or not the sample size will achieve this desired width (Lenth 2001). A popular and often used method for determining the appropriate sample size involves studying the power of a test of hypothesis (Lenth 2001). This method consists of selecting a ...

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