An improved switching rule in variable sampling interval Hotelling´s T2 control chart

In recent years, variable sampling interval (VSI) control charts have been shown to be more efficient than the corresponding fixed sampling interval control charts in detecting process shifts. However, the excessive number of switches between the different sampling intervals is undesirable in the application of the VSI control charts. This paper examines an improved switching rule based on the positions of the past and current samples for the VSI Hotelling´s T² control chart. The performance of the VSI Hotelling´s T² control chart with the improved switching rule is compared with the corresponding VSI Hotelling´s T² control chart without the improved switching rule.