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# Estimating sample size

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.]

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

#### 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.

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