Variable sampling interval X̄ control charts with an improved switching rule

Abstract This paper proposes variable sampling interval X control charts with an improved switching rule which uses a long sampling interval if l2(⩾2) consecutive sample means fall close to centerline and short interval otherwise. A Markov chain approach is used to derive the formulas for evaluating the average time to signal and the average number of switches to signal. Comparisons between the proposed and existing variable sampling interval X control charts indicate that the proposed charts considerably reduce the average number of switches between short and long sampling intervals, while they are comparable with respect to the average time to signal.

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