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.

A new plan is proposed for small‐sample situations using which a one‐third reduction in sample size can be achieved compared to the sample size of an equivalent zero acceptance number single sampling plan. This plan utilises the results of three successive samples for taking decision on...

A table and a procedure are given for finding the single‐sampling quick switching system for which the sum of producer′s and consumer′s risks is minimum for specified Acceptable Quality Level and Limiting Quality Level.

This article provides tables based on the Poisson model for selection of chain sampling plans of type ChSP‐(0,1). The Indifference Quality Level and the Maximum Allowable Percent Defective are the criteria used for fixing the ChSP‐(0,1) plan. Procedures for selection of plans for given...

Purpose The purpose of this paper is to investigate the applicability of Shewhart methodology and other quality management principles to gain a deeper understanding of the observed volatility in stock returns and its impact on market performance. Design/methodology/approach The validity of...

Purpose – Quality function deployment (QFD) is a planning methodology to improve products, services and their associated processes by ensuring that the voice of the customer has been effectively deployed through specified and prioritised technical attributes (TAs). The purpose of this paper is...

This paper extends the concept of chain sampling to variables inspection when the standard deviation of the normally distributed characteristic is known. A discussion of the shape of the known sigma single-sampling variables plan is given. The chain sampling plan for variables inspection will be...