Use the Box-Cox transformation to transform your data to follow a normal distribution and to store the transformed data for further analysis. You can use the Box-Cox transformation only with positive data. If your data include negative values or 0, use the Johnson transformation.
Minitab performs the Box-Cox transformation by default when you select Use all distributions
and transformations on the main dialog box.
- Box-Cox power
transformation (W = Y^λ)
- Select the lambda (λ) value that Minitab uses to transform the data.
- Use optimal
λ: Use the optimal lambda, which should produce the best fitting transformation. Minitab rounds the optimal lambda to 0.5 or the nearest integer.
To use an exact value instead of a rounded value for optimal λ, choose and deselect Use rounded values
for Box-Cox transformations when possible.
- λ = 0 (ln): Use the natural log of your data.
- λ = 0.5 (square
root): Use the square root of your data.
- Other (enter a value
between -5 and 5): Use a specified value for lambda. Other common transformations are square (λ = 2), inverse square root (λ = −0.5), and inverse (λ = −1). In most cases, you should not use a value outside the range of −2 and 2.
- Store transformed data
- Enter a single column of the worksheet to store the transformed values in.
- Subgroups across rows
- If you have subgroups arranged in rows across several columns, enter the columns in the worksheet to store the transformed values in.