A new chart for monitoring service process with unknown distribution

Control charts are effective tools in monitoring both the manufacturing processes and the service processes. Many service processes data came from a process with non-normal distribution or unknown distribution the commonly used Shewhart variables control charts which depend heavily on the normality assumption should not be applied here. Hence an alternative is desired to handle these type of process data. In this paper, we propose a new Mean Chart based on a simple statistic to monitor the process mean shifts. The sampling properties of the new monitoring statistic are explored and the average run lengths of the proposed new chart are calculated. A numerical example of service times from a bank service system with skewed distribution is used to illustrate the proposed Mean Chart. A comparison with two existing charts is also performed. The Mean Chart showed better detection ability than those two charts in detecting the shifts of the process mean.