An improved mean deviation exponentially weighted moving average control chart to monitor process dispersion under ranked set sampling
Quality-control charts are widely used to monitor and detect shifts in the process mean and dispersion. Abbasi and Miller [MDEWMA chart: an efficient and robust alternative to monitor process dispersion, J Stat Comput Simul 2013;83:247–268] suggested a robust mean deviation exponentially
weighted moving average (MDEWMA) control chart for monitoring process dispersion under simple random sampling. In this study, an improved MDEWMA (IMDEWMA) control chart is proposed under ranked set sampling to monitor process dispersion. Detailed Monte Carlo simulations are performed from
symmetric and asymmetric populations to investigate the performances of the proposed and existing control charts in terms of average run length (ARL), median run length and standard deviation of run length. An application to real-life data is also presented to illustrate the use of the IMDEWMA
control chart. It is observed that the IMDEWMA control chart indicates a shift in process dispersion substantially quicker than the MDEWMA control chart, while maintaining comparable ARLs when the process is in control.
Keywords: ARL; EWMA; IMDEWMA; MDEWMA; Monte Carlo simulations; control charts
Document Type: Research Article
Affiliations: Department of Statistics, Quaid-i-Azam University, Islamabad, 45320, Pakistan
Publication date: 02 September 2014
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