Malela-Majika, Jean-ClaudeShongwe, Sandile C.Aslam, MuhammadAbbasi, Saddam A.2022-05-172022-05-172021-07-27Malele-Majika, J.-C., Shongwe, S.C., Aslam, M. et al. 2021, 'Robust distribution-free hybrid exponentially weighted moving average schemes based on simple random sampling and ranked set sampling techniques', Mathematical Problems in Engineering, vol. 2021, art. 4035011, pp. 1-21.1024-123X (print)1563-5147 (online)10.1155/2021/4035011https://repository.up.ac.za/handle/2263/85238This paper proposes new nonparametric hybrid exponentially weighted moving average (HEWMA) control charts based on simple random sampling (SRS) and ranked set sampling (RSS) techniques using the Wilcoxon rank-sum (W) statistic. The in-control robustness and out-of-control (OOC) performances are thoroughly investigated using extensive simulations. The HEWMA W chart is shown to be superior to the basic exponentially weighted moving average (EWMA) and double EWMA W charts in many cases under normal and nonnormal distributions. Moreover, the OOC sensitivities of the new HEWMA W-type control charts are further improved by using supplementary 2-of-2 and 2-of-3 standard and improved runs-rules approaches. It is found that the proposed HEWMA W-type charts with runs-rules perform better than the basic HEWMA W SRS and RSS charts. Real-life data based on the impurity of iron ore are used to illustrate the design and implementation of the new control charts.en© 2021 Jean-Claude Malela-Majika et al. ,This is an open access article distributed under the Creative Commons Attribution License.Nonparametric hybridWilcoxon rank-sumHybrid exponentially weighted moving average (HEWMA)Simple random sampling (SRS)Ranked set sampling (RSS)Article