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...

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...

Abstract. One-sided cumulative sum control charts are constructed for controlling the parameters of a random variable with doubly truncated binomial distribution. It is observed that the average run length (ARL) of the resulting control charts change considerably for a slight shift in the...

Abstract One widely used control chart, the -chart, is based on the assumption that means of samples drawn from the process are normally distributed. When the normality assumption is not valid, control chart users may choose from several different courses of action. These include using Box-Cox...

Abstract Most of the commonly used control charts for variables have been developed under the assumption that the observations are coming from a normal population. One of them is ‘Group Runs’ GR control chart to detect shifts in the process mean proposed by Gadre and Rattihalli (Economic...

Abstract A comprehensive economic cost function is derived for a modified variable sample size and sampling interval (MVSSI) chart. As a variable sample size and sampling interval, a variable sample size, a variable sampling interval, and a static charts are particular cases of an MVSSI chart,...