When a process has proven itself to function at a Six Sigma level this means there are less than ________ defects per million opportunities.

A process operating at a Six Sigma level is defined as having a defect rate of no more than 3.4 defects per million opportunities (DPMO). This widely accepted standard, originating from Motorola, incorporates an empirical observation that processes tend to drift over the long term. A 1.5 sigma shift is factored into the calculation to account for this drift. Therefore, a process that is theoretically capable of 6 sigma performance (where specification limits are six standard deviations from the mean) is expected to perform at a 4.5 sigma level long-term, which corresponds to the 3.4 DPMO figure.

A. 1.7: This value does not correspond to a standard sigma level defect rate within the Six Sigma methodology.
B. 2.6: This is not the recognized DPMO value for a Six Sigma process.
D. 10: This DPMO value corresponds to a process operating at a sigma level of approximately 5.2, which is not the Six Sigma standard.

1. Antony, J., & Banuelas, R. (2002). Key ingredients for the effective implementation of Six Sigma program. Measuring Business Excellence, 6(4), 20-27. In the introduction, the paper states, "The term Six Sigma is defined as a statistical measure of the performance of a process or a product, the rate of 3.4 defects per million opportunities (DPMO)." (Page 20, Paragraph 2). DOI: https://doi.org/10.1108/13683040210451679

2. MIT OpenCourseWare. (2004). 16.851J / ESD.351J Engineering Systems Analysis for Design, Fall 2004. Lecture 10: Six Sigma. The lecture notes explicitly state, "6σ quality = 3.4 defects per million opportunities (DPMO)" and provide a table showing the DPMO for different sigma levels, including the 1.5σ shift. (Slide 10).

3. Tennant, G. (2001). SIX SIGMA: SPC and TQM in Manufacturing and Services. Gower Publishing, Ltd. Chapter 1, "What is Six Sigma?", explains, "A process operating at six sigma will produce 99.99966 per cent of its output, specification-perfect. This is equivalent to 3.4 defects per million opportunities." (Page 5, Paragraph 3).

4. Harry, M. J., & Schroeder, R. (2000). Six Sigma: The Breakthrough Management Strategy Revolutionizing the World's Top Corporations. Doubleday. The book, co-authored by one of the original architects of Six Sigma, defines the 3.4 DPMO standard as the core goal of the methodology. (Chapter 4, "The Six Sigma Breakthrough Strategy").