The deployment of statistical process control in the service process is a prominent global phenomenon in recent years. In this paper, we proposed the optimal variable sample size and sampling interval (VSSI) mean square error (MSE) control chart to monitor the difference between the process mean and the target value and the process variation shifts, and its performance is measured by the average time to signal. From data analyses, we found the optimal VSSI MSE chart that performs better than the specific VSSI and the optimal variable sampling interval and the fixed parameters MSE charts. An example was given to illustrate this new proposed approach. [ABSTRACT FROM PUBLISHER]
