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A nonparametric CUSUM chart for process dispersion

In the present article, we propose a nonparametric cumulative sum control chart for process dispersion based on the sign statistic using in‐control deciles. The chart can be viewed as modified control chart due to Amin et al, which is based on in‐control quartiles. An average run length performance of the proposed chart is studied using Markov chain approach. An effect of non‐normality on cumulative sum S2 chart is studied. The study reveals that the proposed cumulative sum control chart is a better alternative to parametric cumulative sum S2 chart, when the process distribution is non‐normal. We provide an illustration of the proposed cumulative sum control chart.