On valid signals in joint schemes for the process mean and variance
Ralha, T.; Morais, M. C. ; Oliveira, M. Rosário
Economic Quality Control, volume 30, issue 2 (2015), 99-110
https://doi.org/10.1515/eqc-2015-0001
Joint schemes for the process mean and the variance are essential to determine if unusual variation in the location and spread of a quality characteristic has occurred.
This paper comprises a systematic study on the phenomena of misleading, unambiguous and simultaneous signals while dealing with Shewhart and EWMA joint schemes for the process mean and the variance of a normally distributed quality characteristic.
Examples have been added to illustrate how the R statistical software can be used to assess the performance of joint schemes in practice, namely when it comes to the occurrence of those valid signals.
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