Abstract

In recent decades, various adaptive X control charts with various variable parameters such as sampling interval,
sample size, and control limits have been proposed to improve the efficiency of detecting the out-of-control
conditions for small, medium, and large shifts. The variable parameters (VP) adaptive chart is one of these
proposed charts that have an acceptable performance compared to other schemes especially for small shifts. In
this article we proposed a modified version of VP chart with three stage variable chart parameters and have
compared it with some other adaptive charts. Here we used three mostly used indicators to evaluate the
performance of these charts which are Average Time to Signal (ATS), Average Number of Observations to Signal
(ANOS) and Average Number of Samples to Signal (ANSS). Also we have calculated the optimal points for
different adaptive charts and compared them in these points according to the indicators mentioned above.

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