A new distribution-free control chart for monitoring process median based on the statistic of the sign test

Saber Ali*, Zameer Abbas, Hafiz Zafar Nazir, Muhammad Riaz, Muhammad Abid

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Control charts are used to improve the quality of outputs in manufacturing, industrial, and service processes. The parametric control charts produce more false alarms and unacceptable out-of-control signals when the underlying distribution of the process is not normal. Nonparametric/distribution-free control charts are efficient alternatives to overcome the said situation. In this article, the performance of a distribution-free double exponentially weighted moving average (EWMA) chart has been investigated based on the sign test statistic under simple and ranked set sampling schemes. The run-length properties of the proposed charts have been evaluated and compared with nonparametric EWMA sign, parametric EWMA, and parametric double EWMA control charts, using different run-length measures. The comparison reveals the efficiency of the proposed chart over its alternatives in detecting small and medium shifts in the process location. A real-data application using the substrate manufacturing process has been provided to show the implementation of the proposed chart.

Original languageEnglish
JournalJournal of Testing and Evaluation
Issue number1
StatePublished - 1 Jan 2022

Bibliographical note

Publisher Copyright:
Copyright © 2021 by ASTM International.


  • Control chart
  • Double exponentially weighted moving average chart
  • Manufacturing process
  • Nonparametric
  • Ranked set scheme
  • Run-length measures
  • Sign statistic

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering


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