# Six Sigma = 3.4 DPMO … Why?

• /
• Blog
• /
• Six Sigma = 3.4 DPMO … Why?

I have often been asked, why do we have 3.4 Defects Per Million Opportunities (DPMO) for a Six Sigma process?

Before I talk about Six Sigma, let's talk about the process control with plus-minus three sigmas. Historically processes were controlled in $$\pm 3\sigma$$, and this was the basis of control charts.

When you have a process, which is centered around the mean, it will have 99.73% items within $$\pm 3\sigma$$ and will have 0.27% items outside the $$3\sigma$$ limits. Out of this 0.27 %, you will have half of the rejection (0.135%) on the lower end and another half rejection on the upper end. See the Normal Distribution curve below:

15.99

##### Green Belt

Perform medium size improvement projects.

Aligned with ASQ CSSGB Body of Knowledge.

$15.99 ##### Black Belt Master the Six Sigma tools to lead improvement teams. Aligned with ASQ CSSBB Body of Knowledge.$

39.99

If for example, the process shifts $$1.5 \sigma$$ to the right, then we will be left with $$4.5 \sigma$$ (6.0 - 1.5) as the acceptance area in the right and $$-7.5 \sigma$$ ( -6.0 - 1.5) on the left. With this shift, the rejection rate will be 3.4 DPMO. Similarly taking the other extreme case, where the process moves $$1.5 \sigma$$ to the left then also the rejection rate will be 3.4 DPMO. Both these cases are the worst case scenarios. Hence Six Sigma process has the maximum defects as 3.4 DPMO. See the calculations for $$1.5 \sigma$$ to the right, shown below:

Above plots were made using R Programming, and show the Normal Distribution curve with plus-minus three sigma limits only. However, the rejection area calculation is shown at the top of the chart. You can verify these numbers using the Normal distribution table or other software such as Microsoft Excel or Minitab.

\$85  SALE

###### Six Sigma Green Belt  (SALE)

Fully aligned with ASQ Certified Six Sigma Green Belt (CSSGB) 2022 Body of Knowledge. Includes Minitab 18 examples.

About the Author

 (adsbygoogle = window.adsbygoogle || []).push({}); 

Customers served! 1

Quality Management Course

FREE! Subscribe to get 52 weekly lessons. Every week you get an email that explains a quality concept, provides you with the study resources, test quizzes, tips and special discounts on our other e-learning courses.

Similar Posts:

June 8, 2022

## ASQ® CSSGB Body of Knowledge 2022 – What is New?

ASQ® CSSGB Body of Knowledge 2022 – What is New?

October 23, 2022

## A Beginner’s Guide to Machine Learning for Quality Professionals

A Beginner’s Guide to Machine Learning for Quality Professionals

January 19, 2022

## 10 Reasons Organizations Do Not Implement Six Sigma

10 Reasons Organizations Do Not Implement Six Sigma

December 2, 2021

## RADPAC Model of Negotiation

RADPAC Model of Negotiation

December 24, 2021

## Seven Quality Tools – Scatter Diagram

Seven Quality Tools – Scatter Diagram

May 27, 2018

## A Quick Guide to ISO Standards

A Quick Guide to ISO Standards

May 20, 2019

## Japanese Quality Management Terms – Flash Cards

Japanese Quality Management Terms – Flash Cards

November 24, 2022

## Is Six Sigma the Cure for Healthcare’s Ailing Quality Problem?

Is Six Sigma the Cure for Healthcare’s Ailing Quality Problem?

May 11, 2019

## ASQ® CSSGB [2022] | How to pass your Six Sigma Green Belt Exam?

ASQ® CSSGB [2022] | How to pass your Six Sigma Green Belt Exam?

32 Courses on SALE!