Box-Cox transformation

power transformation towards normality

y = (x^λ − 1) / λ

Transforms positive, skewed data with a power λ so that it becomes approximately normal; capability is then calculated on the transformed scale with transformed limits. Fitting a distribution directly (ISO 22514-2 percentile method) is often easier to explain.

Calculate it

Process Capability & Control Charts: Cp, Cpk, Pp, Ppk, PPM and confidence intervals with X-bar/R, X-bar/S or I-MR charts and all 8 Nelson rules.

Related terms

• Anderson-Darling test: normality test with weight on the tails