Distribution-Free Phase I Control Charts for Subgroup Location


Jones-Farmer, L. Allison; Jordan, Victoria; Champ, Charles W.   (ASQ)   Auburn University; M. D. Anderson Cancer Center; Georgia Southern University

Journal of Quality Technology    Vol. 41    No. 3
QICID: 30230    July 2009    pp. 304-316
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Article Abstract

[This abstract is based on the authors' abstract.] Statistical quality control often relies on the completion of a Phase I study. Many Phase I control charts, however, rely on an assumption of normally distributed process observations that may not be reasonable in the early stages of process control. A literature review shows no purely distribution-free Phase I control chart methods currently exist. This study introduces a distribution-free method for defining the in-control state of a process and identifying an in-control reference sample that can be used to estimate the process parameters for a Phase II procedure. The proposed procedure compares favorably with the traditional X-bar chart when the process is normally distributed and better than the X-bar chart when the process distribution is skewed or heavily tailed.


Design of control charts; Nonparametric methods; Shewhart control chart; Statistical process control (SPC)

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