Nonparametric Shewhart-type Quality Control Charts in Fuzzy Environment

Nonparametric control charts are presented in order to figure out the problem of detecting changes in the process median (or mean)‎, ‎or changes in the variability process where there is limited knowledge regarding the underlying process‎. ‎When observations are reported imprecise‎, ‎then it is impossible to use classical nonparametric control charts‎. ‎This paper is devoted to the problem of constructing nonparametric control charts in presence of fuzzy data and parameters‎. ‎For this aim‎, ‎we propose two different methods‎: ‎Dp,q -distance between fuzzy numbers and credibility measure for ranking fuzzy data‎, ‎that can be used to construct sign and Wilcoxon signed-rank control charts‎. ‎Then‎, ‎this statistical control charts are applied to monitor location and scale parameters of a continuous statistical process‎. ‎Finally‎, ‎proposed control charts application is evaluated with numerical examples.