One-Sided Variable Sampling Interval Control Chart for Monitoring the Coefficient of Variation

The regular practice of using a coefficient of variation (CV) control chart is achieved by collecting the samples at a fixed sampling interval (FSI). Recently, various studies showed that the detection efficiency of a control chart in monitoring shifts in the CV can be enhanced by implementing the variable sampling interval (VSI) strategy. However, these studies also showed that the adaptive charts, such as the VSI chart, are ineffective in detecting a decrease in the CV. As a remedy to this problem, a one-sided VSI chart that is effective in monitoring the increase in the CV is required. Therefore, this paper proposes a one-sided VSI CV chart and compares its performance with the two-sided VSI CV chart. For monitoring an increase in the CV, we revealed that the one-sided VSI CV chart has a superior performance compared to the two-sided VSI CV chart.