Wilcoxon Signed Rank Test in Excel using the QI Macros

When to Use the Wilcoxon Signed Rank Test

A Wilcoxon Signed Rank test compares the differences between two paired samples to determine if the data is symetrical. If so, the median difference would be close to zero. If not, the data is asymetrical. Consider the following example.

Test Example

Imagine a credit union would like to loan more money. And that they think having more detailed information on the loan application results in larger loans. (From Applied Statistics, John Neder.) Using data from 20 loan officers on case studies with limited and detailed information, they determine the amount of money loaned:

Hypothesis Test: Since p (0.001) is less than alpha (0.05) reject the null hypothesis that the two levels of detail result in the same loan amount. So, if the credit union wants to loan more money, get more detail.

Wilcoxon 1-Sample Test

The same type of test can be applied to one-sample and compared to an expected median. The following example compares light bulb life to a median of 2500 hours:

Hypothesis Test Results: At alpha = 0.05 we reject the null hypothesis because p (0.027) < 0.05. The bulb life, in this case, has a median greater than 2500.

Watch Non-parametric tests in Excel Video

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

• Overvew of all hypothesis tests in Excel
• Other Nonparametric tests in Excel in the QI Macros

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