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Sample Size Determination-ECO6416

Sample Size Determination-ECO6416 - Sample Size...

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Sample Size Determination At the planning stage of a statistical investigation, the question of sample size (n) is critical. This is an important question therefore it should not be taken lightly. To take a larger sample than is needed to achieve the desired results is wasteful of resources, whereas very small samples often lead to what are no practical use of making good decisions. The main objective is to obtain both a desirable accuracy and a desirable confidence level with minimum cost. Students sometimes ask me, what fraction of the population do you need for good estimation? I answer, “It’s irrelevant; accuracy is determined by sample size." This answer has to be modified if the sample is a sizable fraction of the population. The confidence level of conclusions drawn from a set of data depends on the size of the data set. The larger the sample, the higher is the associated confidence. However, larger samples also require more effort and resources. Thus, your goal must be to find the smallest sample size that will provide the desirable confidence. For an item scored 0 or 1, for no or yes, the standard error (SE) of the estimated proportion p, based on your random sample observations, is given by: SE = [p(1-p)/n] 1/2 where p is the proportion obtaining a score of 1, and n is the sample size. This SE is the standard deviation of the range of possible estimate values.

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