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 etal, 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 S-2 chart is studied. The study reveals that the proposed cumulative sum control chart is a better alternative to parametric cumulative sum S-2 chart, when the process distribution is non-normal. We provide an illustration of the proposed cumulative sum control chart.