Overview for Box-Cox Transformation

A Box-Cox transformation of your process data can help correct the following conditions:

The process data are not normally distributed, especially if the data are not collected in subgroups. For more information, go to Normality assumptions for control charts.
Subgroup variance is unstable because the variation in the data is proportional to the subgroup mean.

You can also perform a Box-Cox transformation when you create a control chart. For example, to transform the data when you create an Xbar-R chart, choose Stat > Control Charts > Variables Charts for Subgroups > Xbar-R > Xbar-R Options > Box-Cox.

Where to find this command

To perform a Box-Cox transformation, choose Stat > Control Charts > Box-Cox Transformation.

When to use an alternate analysis

If you have data values less than 0, use a Johnson Transformation.

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