Abstract In the statistical process control literature, counts of nonconforming items are frequently assumed to be independent and have a binomial distribution with parameters (n,p) , where 𝑛 and 𝑝 represent the fixed sample size and the fraction nonconforming. In this paper, the...

Purpose – This paper seeks to propose a univariate robust control chart for location and the necessary table of factors for computing the control limits and the central line as an alternative to the Shewhart X¯ control chart. Design/methodology/approach – The proposed method is based on two...

“Twin metric” control preserves the simple, intuitive graphical features of Shewhart control charts, while incorporating the much improved performance of CUSUM. Two metrics are plotted on the twin metric control chart at each sample interval; the Shewhart value and a simplified CUSUM value....

Purpose – The majority of quality control charts are employed for normally distributed data. In reality this assumption is not always valid. This paper aims to consider an alternative the truncated normal. Design/methodology/approach – Having derived integral equations for the average run...

Purpose – The majority of quality control charts are employed for normally distributed data. In reality this assumption is not always valid, as an alternative the Burr distribution is considered here. Design/methodology/approach – Having previously derived integral equations for the average...

Abstract Some recent studies have proved that charts with variable sample size ( VSS ) detect moderate or larger shifts in normal and stable processes more quickly than the Standard Shewhart ( SS ) chart. But the statistical efficiency of charts, the speed at which they detect smaller shifts of...

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 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.

Abstract Imprecise measurements may seriously affect the efficiency of process control and production cost. For two dependent processes, the in-coming quality variable in the first process may influence the out-going quality variable in the second process. To effectively monitor and distinguish...