Geometric Q Charts for High Quality Processes

Article

Quesenberry, Charles P.   (1995, ASQC)   North Carolina State University, Raleigh, NC

Journal of Quality Technology    Vol. 27    No. 4
QICID: 11420    October 1995    pp. 304-315
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Article Abstract

The geometric distribution based on the inverse binomial method of sampling is used to define Q statistics for the case when the process fallout p is known and when it is not known in advance of sampling. The effectiveness to detect shifts in p of four tests made on Shewhart Q charts of these statistics as well as both exponentially weighted moving average and cumulative sum Q charts computed from these statistics is studied. The classic test of one point outside 3-sigma control limits is found t have poor sensitivity to detect a one-step permanent shift in p. The test consisting of four-out-of-five points beyond one standard deviation is found to be a good general omnibus test on a Shewhart Q chart to detect an increase or decrease in p.

Keywords

Attributes control charts,Cumulative sum control chart (CUSUM),Exponentially weighted moving average control charts (EWMA),Q chart (quality score),Shewhart control chart


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