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    Estimating sample size

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    You are studying the effect of two different methods of relaxation therapy. These two have never been compared before. The population mean for method 1 is 100 on a standardized score of relaxation. The population mean for method 2 is 102 on the same standardized test. The population standard deviation for both methods is 5. Assume that you want a power of .9 to detect an effect in your study. Estimate the sample size. [Assume alpha (significance level) equals 0.05.]

    Possible Answers....

    A. Total N is greater than 300
    B. Total N = 264
    C. Total N is less than 526
    D. n in each group is 526

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    Solution Preview

    A: The formula that I found to calculate sample size, for a 2-sample t-test, is as follows

    n= [2 * sigma^2 * (z(alpha/2) + z(beta))^2]/delta^2.

    sigma^2 is the variance.
    delta is the smallest difference between means.
    alpha is the ...

    Solution Summary

    Given certain parameters (mean and standard deviation) one can estimate the sample size needed in order to reach a certain level of power. We have an example that illustrates just how to do this. A step-by-step solution has been provided. A Word Doc is attached, which is in depth and has clear mathematical notation.