Question: Do the data have to be normally distributed for Process Behavior Charts to be valid?

A reader asked:

“Do the data have to be normally distributed to use a Process Behavior Chart?”

The short answer is “no.”

Process Behavior Charts, as a form of “control chart,” are very robust and it doesn’t matter what the underlying statistical distribution of your metric is over time.

For more, read this article by Donald J. Wheeler, Ph.D.:

Myths About Process Behavior Charts

“Myth One: It has been said that the data must be normally distributed before they can be placed on a process behavior chart.”

“Shewhart then went on to note that having a symmetric, bell-shaped histogram is neither a prerequisite for the use of a process behavior chart, nor is it a consequence of having a predictable process.”

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