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A CUSUM for a Scale Parameter

Summary: Standard CUSUM procedures are available for controlling the mean of a process. However, in many industrial applications it is important to control the process variability as well. This article presents a technique for employing the same CUSUM procedure used for the mean for controlling the variance. The technique is based on cusumming | Xi / sigma| 1/2, which is very nearly normally distributed if X is N(O, sigma-squared). If the process has a nonzero unknown mean, then the same technique may be applied with Xi replaced by the difference between successive observations.

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  • Topics: Change Management
  • Keywords: Control charts,Regression,Change management,Scale parameter,Cumulative sum control chart (CUSUM)
  • Author: Hawkins, Douglas M.
  • Journal: Journal of Quality Technology