SKEWNESS CORRECTED CONTROL CHARTS: A NEW PROBABILITY MODEL

Abstract

In the industry, control charts are powerful statistical tools for process control. Shewhart control charts assume a Normal Distribution for the quality characteristic. On the basis of sample size n, if ‘t_n’ is a statistic, Shewhart variable control charts have control limits  In the case of a skewed population, control limits must be constructed using a different method. A skewness correction method has been used to construct control charts for mean and range by several researchers.

By adopting the popular probability model Exponentiated Inverse Rayleigh Distribution (EIRD), this paper attempts to construct a control chart with skewness corrected, using EIRD. Using coefficients of skewness techniques Bowley's and Kelly's as a basis, we construct “variable control charts for the mean and range of subgroups in EIRD”. Coverage probabilities are also calculated based on the simulation technique. The findings are compared with the methods of EIRD and other existing models.