How to Perform a Normality Test on Minitab

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Before beginning to perform any statistical analysis of the given data, it is important to determine whether the data follows a normal distribution. If the data provided follows a normal distribution, you can use parametric tests (test of means) for additional levels of statistical analysis. If the data provided does not follow a normal distribution, you should use nonparametric tests (median test). As we all know, parametric tests are more powerful than non-parametric tests. Therefore, verifying the normality of the data provided becomes even more important.

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    Write a hypothesis. A good way to perform any statistical analysis is to start by writing a hypothesis. For a normality test, the null hypothesis is “The data follows a normal distribution” and the alternative hypothesis is “The data does not follow a normal distribution.”

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    Select data. Select and copy the data from the spreadsheet on which you want to test for normality.

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    Paste the data into a Minitab worksheet. Open Minitab and paste the data into the Minitab worksheet.

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    Press “Statistics”. On the Minitab menu bar, click Statistics.

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    Click on “Basic Statistics”.


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    Click on “Test for normality”

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    Select data. A small window called “Normal Test” will appear on the screen. Click on an available option within the white box, then click “Select.”

    • Note that “VariableThe ” tab will have the name of the selected data.
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    • Also note that “Anderson-Darling” is already selected under “Tests for Normality”. Anderson-Darling is the most widely used normality test. Therefore, the default test selection for normality in Minitab is “Anderson-Darling”.
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    Press OK.”

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    Understand the p-value shown on the normal probability plot. A normal probability plot will appear on the screen.

    • Note whether the p-value shown on the normal probability plot is greater than 0.05 or less than 0.05.
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    Conclude the results. As described in the hypothesis writing step, if we do not reject the null hypothesis, the conclusion will be “The data follow a normal distribution.” If we reject the null hypothesis, the conclusion will be “The data do not follow a normal distribution.” Let’s relate the p-value to the written hypothesis.

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    Do not reject the null hypothesis if the p-value is greater than 0.05. If the observed p-value on the normal probability plot is greater than 0.05, we cannot reject the null hypothesis. Therefore, the conclusion is “The data follow a normal distribution.”

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    Reject the null hypothesis if the p value is less than 0.05. If the observed p-value on the normal probability plot is less than 0.05, we reject the null hypothesis. Therefore, the conclusion is “The data do not follow a normal distribution.”

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Categories: How to
Source: HIS Education

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