Optimum sample size and sampling interval for controlling the mean of non-normal variables

Following Duncan [3], the per hour cost of the process under the surveillance of a mean chart for controlling the mean of non-normal variables whose density function is represented by the first four terms of an Edgeworth series is obtained. The sample size and sampling interval which minimize the cost for detecting a particular shift in the process average are derived when the width of the control limits is specified. They are numerically determined for different non-normal situations by assuming various cost values when a particular shift in the process average is to be detected. They are presented in a table which compares the changes in optimum sample size and sampling interval due to changes in (a) the non-normal situation, (b) the shifts to be detected in the process average and (c) width of the control limits specified. © Taylor & Francis Group, LLC.