Abstract This article provides an argument against the use of three sigma limits for control charts. An alternative proposal to use control limits narrower than three sigma control limits is made. The main reason for narrowing the control limits is to achieve a smaller variability in the...

Abstract Using a counter example, we show that the formula for computing the Average Run Lengths (ARL) of a moving average control chart (MA) in Wetherill and Brown (1991) is incorrect. However, we conjecture that the formula may provide an upper bound for the ARL of a moving average control chart.

Abstract Average run length is the most popular measure to assess the statistical performance of a control chart procedure. This paper discusses the limitations of the traditional average run length measure and introduces the concept of ‘unity’ average run length which is the ratio of the...

Abstract The reduction of run length variability has received little attention in the statistical process control literature. This note proposes a modification of the signal rule for the EWMA control chart resulting in a reasonable reduction of run length variability.

In this paper, the concept acceptance number has been incorporated to the single level continuous sampling plan CSP-1. The advantage of the proposed plan, designated as the CSP-C plan, is to achieve a reduction in the average fraction inspected at good quality levels. Nomographs for the design...

In this paper, a modification is proposed on the tightened two-level continuous sampling plan. The tightened two-level plan is one of the three tightened multi-level continuous sampling plans of Derman et al. (1957) with two sampling levels. A modified tightened two-level continuous sampling...

For high-quality processes, non-conforming items are seldom observed and the traditional p (or np) charts are not suitable for monitoring the state of the process. A type of chart based on the count of cumulative conforming items has recently been introduced and it is especially useful for...

High-yield production processes that involve a low fraction non-conforming are becoming more common, and the limitations of the standard control charting procedures for such processes are well known. This paper examines the control procedures based on the conforming unit run lengths applied to...