Title: A modified control chart for monitoring non-normal characteristics

Authors: Boby John; S.M. Subhani

Addresses: SQC & OR Unit, Indian Statistical Institute, 8th Mile, Mysore Road, Bangalore, 560 059 India ' SQC & OR Unit, Indian Statistical Institute, Street # 8, Habsiguda, Hyderabad, 500 007 India

Abstract: A process in control and capable of meeting customer requirements can enhance the survival and growth of the business. The systematic use of process improvement methodologies like lean, six sigma, etc., can improve the capability of the process significantly. When the process is highly capable, sometimes it may not make business sense to monitor the process using traditional control charts. It may be better to allow the process mean to vary over a small interval provided the fraction non-conforming is within a pre-specified value. This can be achieved by monitoring the process using the modified control chart. Most of the research on modified control chart discuss the case of normally distributed characteristics. In this paper, the authors extend the modified control chart methodology to monitor non-normal characteristics. The approach is based on Johnson's system of distributions. The suggested methodology is also demonstrated using two case studies in the paper.

Keywords: statistical process control; modified control chart; non-normal characteristics; process capability analysis; Johnson's system of distributions.

DOI: 10.1504/IJPQM.2020.105990

International Journal of Productivity and Quality Management, 2020 Vol.29 No.3, pp.309 - 328

Received: 23 Oct 2018
Accepted: 08 Dec 2018

Published online: 10 Mar 2020 *

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