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Box-Cox Transformation Help

This page shows how to perform the Box-Cox Transformation using SPC for Excel. The data used can be downloaded at this link.

Running the Box-Cox Transformation

Note: for individual values, the average moving range is used to estimate the standard deviation

Box-Cox Transformation Output

Two sheets are added to the workbook. Both are named with a number following the name reflecting the number of times the Box-Cox transformation has been run in the workbook.

Box Cox Plot

This sheet contains a chart of sigma vs lambda along with the optimum lambda, the rounded lambda, the confidence limits for lambda as shown below. The red lines are the confidence limits.

Box Cox Output

The top part of the worksheet contains the descriptive statistics as well as the Anderson-Darling statistic and p value. If the p value is less than 0.05, the distribution is not normally distributed. The lambda results are also given.

The middle part of the worksheet contains the histograms and P-P plots (if those options were selected).

The bottom part of the worksheet contains the transformed data if that options was selected.

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