Using the Power and Sample Size tool for a 2-Sample t-test

Here, we will use the power and sample size tools to find the number of samples needed to observe a difference in the means between two populations.

We will not need to open a dataset for this recipe. Using a standard deviation that has been set to 1, we will discover the number of samples required to observe a 1, 2, or 3 standard deviation difference between two population means.

How to do it…

The following steps will help us find the sample size required to detect differences of 1, 2, or 3 standard deviations between the means of two samples:

  1. Go to the Stat menu and then Power and Sample Size and then select 2 Sample t….
  2. Fill out the dialog box as shown in the following screenshot:
    How to do it…
  3. Click on OK.

How it works…

The differences are stated in terms of the value of the standard deviation from the results shown in the following screenshot:

How it works…

To observe a 1 standard deviation difference between the population means of two samples, we would need 17 samples to have an 80 percent chance of observing this difference or 23 samples to have a 90 percent chance of observing the difference. This sample size is for both groups of data.

The options for this test allow us to specify a one-sided test or change the significance level.

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