Two Charts: Not One
- Quality Engineering
- April 2007
- Volume 19 Issue 2
- pp. 93-100
- Box, George E. P., Paniagua-Quinones
- University of Wisconsin, Madison
[This abstract is based on the authors' abstract.]Because data coming from a typical operating process do not vary about a fixed mean, the operation of traditional control charts may be inconsistent. It is shown that a nonstationary model provides a continuously updated local mean level that can be used to produce both a bounded adjustment chart for determining when to adjust the process to achieve maximum economy and a Shewhart monitoring chart identifying assignable causes of trouble applied to the deviations from the local mean. Estimation of the mean and standard deviation are not required.