请教：为什么要用box-cox Transformation，意义何在；以及使用条件

The Box-Cox transformation can be useful for correcting both nonnormality in process data and subgroup process variation that is related to the subgroup mean. Under most conditions, it is not necessary to correct for nonnormality unless the data are highly skewed. Wheeler and Wheeler and Chambers suggest that it is not necessary to transform data that are used in control charts, because control charts work well in situations where data are not normally distributed. They give an excellent demonstration of the performance of control charts when data are collected from a variety of nonsymmetric distributions.