Title: The expanded DPMO interface for capturing the compounding effect of process mean and variability as a new paradigm for process evaluation and improvement

Authors: Russell Krenek; Byung Rae Cho

Addresses: Department of Industrial Engineering, Clemson University, Clemson, SC 29634, USA ' Department of Industrial Engineering, Clemson University, Clemson, SC 29634, USA

Abstract: This paper explores the gap between the existing conceptual notion of defects per million opportunities (DPMO) as part of process improvement initiatives and its applications to real-world engineering processes. The current way of obtaining the DPMOs documented in the literature is problematic since it strictly assumes that there will be a shift in the process mean over time, while process variability remains unchanged. Accordingly, it does not account for shifting process standard deviation. This may not be the case in real-world practices. This paper offers several unique contributions to the Six Sigma body of knowledge by expanding the existing DPMO and process fallout concepts, ultimately leading to process improvement. First, this paper considers the process fallout resulting from shifting standard deviation while keeping the mean the same. Second, the process fallout is examined when shifting both the process mean and standard deviation over time. Third, standard process capability indices are then modified to incorporate both mean and standard deviation shifts. Finally, the paper is extended to dual quality characteristics to obtain a better understanding of the integrated effects of correlations on the DPMO and process fallout.

Keywords: DPMO; defects per million opportunities; process fallout; six sigma; process capability indices; shifting process mean; process variability; process evaluation; process improvement; shifting standard deviation; deviation shifts; quality control.

DOI: 10.1504/IJSSCA.2015.074963

International Journal of Six Sigma and Competitive Advantage, 2015 Vol.9 No.2/3/4, pp.174 - 207

Received: 30 Jan 2015
Accepted: 20 Dec 2015
Published online: 27 Feb 2016 *

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