Lean and Six Sigma

January 1, 2020
By Darren Dolcemascolo

One can spend an inordinate amount of time debating on online forums about the merits of Lean versus Six Sigma.  However, much of the time spent on this debate is wasted.  I do not believe Six Sigma versus Lean is actually a contest.  Both methodologies (or management systems) have merit and have been used successfully.  The question is: do we need to use both of them to have a successful improvement system in organizations?  If so, when and how?  

I firmly believe in the saying "there is more than one way to skin a cat."  I do not believe it is necessary to use both Lean and Six Sigma.  I think the Lean Management system can be used very successfully on its own; however, I also think both Lean and Six Sigma can be used together with much success. 

Let's define our terms.  When I use the term "Lean",  I am referring to the Toyota Production System / Toyota Way.  (I realize there has been much debate recently as to what Lean is versus the Toyota Production System, but please let us ignore that for now.  Originally, "Lean Production" was used to describe Toyota's system.)  Lean is a continuous improvement philosophy of providing the customer with a defect free product or service when it is needed and in the right quantity through the elimination of waste.  Lean includes the concepts of Continuous Flow, Pull, Built in Quality, and Basic Stability. Perhaps, most importantly, Lean includes the idea of building a culture of "Respect for People."  While there are many Lean "tools", the problem solving process now known as A3 Problem Solving (or Toyota Business Practices) is absolutely central to becoming Lean.  This is how kaizen (continuous improvement) is accomplished in a systematic manner over time.

What about Six Sigma?  Six Sigma is aimed at achieiving better quality / less variation in processes.  It also has a "problem solving" process called DMAIC (Define Measure Analyze Improve Control), which is central to Six Sigma.  Six Sigma has a focus on understanding what the customer needs (Voice of the Customer), measuring how well the current process meets those needs, determining which factors or causes need to be addressed or improved to improve the process, and implementing and monitoring/sustaining the improved process. There are many tools of Six Sigma, almost all of which pre-date it.  Some of the tools of Six Sigma are statistical methods while others are more qualitative tools.  There are also some tools that are taught as part of Lean as well as Six Sigma (such as a Fishbone/Cause and Effect Matrix).

The question should not be: Should I use Lean or Six Sigma?  Rather, the question should be: "What kind of system do we need to develop in order to improve our business?  I believe there are four basic requirements for a successful improvement system:

1. A problem solving process that permeates the organization.  Everyone must understand and practice it.  I believe this can be Toyota Business Practices/A3 or DMAIC.  A problem is defined as the gap between the current condition and the target condition or standard; a problem solving process aims to identify the root cause or critical causes and then identify, test, and implement countermeasures to address the causes.

2. There must be one or more ways in which the organization utilizes the problem solving process to make improvements.  In the Six Sigma world, there are DMAIC projects.  With Lean, we have Daily Kaizen, Kaizen Events, and other A3 "projects."  Some combination of these should be taught and practiced.

3. A set of tools from which problem solvers can utilize as needed.  Depending on the nature of the business, statistical methods such as those taught in six sigma may be useful.  General problem solving tools will almost always be useful, and several Lean/TPS tools will be useful.

4. A methodology for Developing and Aligning Goals and Measuring to those Goals must be in place.  I don't believe that improvement efforts should be purely cost-cutting efforts.  An organization should use Strategy Deployment to develop goals and identify the right initiatives/projects to work on.  Value Stream Mapping is also a methodology that can be used at a high level to identify the right improvement activities on which to focus.  Success should be measured based on the key metrics identified- not purely on cost savings. 

I believe Lean, Six Sigma, and Lean Six Sigma practitioners should recognize that there are several ways to make improvements to a business.  We need to be open to the idea that there are often multiple ways to achieve our goals.  Utilizing the basic 4 requirements above, a system that can achieve success can be built in any organization.

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