A comparison of some modified confidence intervals based on robust scale estimators for process capability index

  • Moustafa Omar Ahmed Abu-ShawieshEmail author
  • Shipra Banik
  • B. M. Golam Kibria
  • Hayriye Esra Akyüz
Production Process


This paper aims to compare the performances of modified confidence intervals based on robust scale estimators with classical confidence interval for process capability index (Cp) when the process has a non-normal distribution. The estimated coverage probability and the average width of the confidence intervals were obtained by a Monte-Carlo simulation under different scenarios. Simulation results showed that the modified confidence intervals performed well in terms of coverage probability and average width for all cases. Two real-life numerical examples from industry are analyzed to illustrate the performance and the implementation of the classical and modified confidence intervals for the process capability index (Cp) which also supported the results of the simulation study to some extent.


Confidence interval Coverage probability Average width Process capability index Quality engineering Statistical process control 



Authors are grateful to two anonymous referees and editor in chief for their invaluable constructive comments and suggestions, which certainly improved the quality and presentation of the paper greatly.


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Copyright information

© German Academic Society for Production Engineering (WGP) 2019

Authors and Affiliations

  • Moustafa Omar Ahmed Abu-Shawiesh
    • 1
    Email author
  • Shipra Banik
    • 2
  • B. M. Golam Kibria
    • 3
  • Hayriye Esra Akyüz
    • 4
  1. 1.Faculty of Science, Department of MathematicsThe Hashemite UniversityAl-ZarqaJordan
  2. 2.Department of Physical Sciences, School of Engineering and Computer Science, BashundharaIndependent UniversityDhakaBangladesh
  3. 3.Department of Mathematics and StatisticsFlorida International UniversityMiamiUSA
  4. 4.Faculty of Science and Arts, Department of StatisticsBitlis Eren UniversityBitlisTurkey

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