Exponential Weighted Moving Average (EWMA) Chart Under The Assumption of Moderateness And Its 3∆ Control Limits

Abstract

Moderate distribution is a very good alternative of normal distribution proposed by Naik V.D and Desai J.M. [4], which has mean deviation as scale parameter rather than the standard deviation. Mean deviation (δ) is a very good alternative of standard deviation (σ) as mean deviation is considered to be the most intuitively and rationally defined measure of dispersion. This fact can be very useful in the field of quality control to construct the control limits of the control charts. On the basis of this fact Naik V.D. and Tailor K.S. [5] have proposed 3δ control limits. In 3δ control limits, the upper and lower control limits are set at 3δ distance from the central line where δ is the mean deviation of sampling distribution of the statistic being used for constructing the control chart. In this paper it has been assumed that the underlying distribution of the variable of interest follows moderate distribution proposed by Naik V.D and Desai J.M. [4] and 3δ control limits of exponential weighted moving average chart are derived. Also an empirical study is carried out to illustrate the use these charts.