Levenes Test in Excel using the QI Macros

Levene's Test compares two or more independent sets of test data. It helps determine if the variances are the same or different from each other. The Levene's Test is like the f test. However, the Levene's test is robust enough for non-normal data and handles more than two columns of data. Consider the following example.

Watch this Levene's Test in Excel Video

Levene's Test - two sample example

If you're producing rubber made with two different recipes, you might want to know if the variances in tensile strengths are the same or different (Juran's QC Handbook 4th pg 23.74):

• The null hypothesis (H₀) - variances are the same
• The alternate hypothesis (H_a) - variances are different

Now, conduct a test and enter the data into Excel:

Select the data with the mouse and click on the QI Macros Menu to select Levene's test:

The Levene's test macro will calculate the results with the F-test and will interpret the results for you.

Interpreting the Levene's test results

Since Levene's p value > a ( 0.337> 0.05), we can accept the null hypothesis that the variances are equal.

While an F test works well on two-samples of normal data, it isn't robust enough to handle non-normal data or more than two samples. (Notice that Levene's p value differs from F Test's two-tailed value of 0.305; however both cause acceptance of null hypothesis.)

Levene's Test - ten sample example

Now, consider the following example of ten batches of gear diameters:

Again the p-value 0.099 > 0.05, so we accept the null hypothesis that variances are equal from a batch to batch.

Levenes test is just one of the tests included in the QI Macros Statistical Process Control software. Other tests include:

• f test - Two Samples
• t test assuming equal variances
• t test assuming unequal variances
• t test one sample
• ANOVA - Analysis of Variance
• Overvew of all hypothesis tests in Excel

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