SOCR EduMaterials AnalysisActivities NormalPower Power Random

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SOCR Normal Power Activity: Look for Power with Generated Data, Background

With two parent distributions, both of the same standard deviation (sigma), and we already know the power we want, we'd like to find the sample size needed. The significance level needs to be provided by the user.

The two hypotheses are written as:

H_0 the true mean, mu, is equal to some constant, mu_0.

H_A: the true mean, mu, is not equal to mu_0. And we are testing for another possible mean, mu_A.

Note that, H_A can be testing the cases of mu_0 > mu_A, and mu_0 < mu_A. The options are also provided by this tool.

SOCR Normal Power Activity: Look for Power with Generated Data, Example

You'll first need to tell the computer to generate some data for you. The distribution's paramters (mean and standard deviation) are calucluated from the randomly generated data. The sample size is computed as well. And then, you need to input the mean for the alternative hypothesis for the power of the test.

1. Click on DATA and then RANDOM EXAMPLE to generate random data.

2.The result will not be computed until you tell the computer which column of the data you'd like to compute for. So, if you clikc on CALCULATE, you'll see an error message like this.

Just click on MAPPING and you'll see a screen like below. Here, we only have one column, X. Click on ADD to include X for compuation.

3. After you do the mapping, the mean and standard deviation of the data are calculated and show in the SELECT PARAMETER panel.

But we don't have the mean for the alternative yet, neither have we determined what type of hypothesis testing (less than? greater than? not equal to?) to use. So, if you click CALCUALTE without inputting everything in the SELECT PARAMETERS panel, you'll see an error message.

4. Be sure to select Get Power Using Sample Size. Have all the fields filled out, and then click on CALCULATE and then RESULT, the results are given.

5. Click on the GRAPH button to see a function of possible values of power.

6. Also, click on the COMPARE CURVES to see the data, the population, and distribution of mean.

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