We are often asked, “Which improvement approach, Lean or Six Sigma, is better?” “What are the main differences?” While I know these questions have and continue to be debated by both Lean and Six Sigma practitioners, I want to have a “lite” discussion on the topics of Lean and Six Sigma. Specifically, by the end of this discussion, I hope you have a better understanding of the unique characteristics of both Lean and Six Sigma.
To start things off let us go ahead and debunk some myths. Specifically, some continuous improvement practitioners like to say that Lean is all about eliminating waste while reducing the time it takes to do a task and Six Sigma is about improving quality and reducing variation.
What complicates matters even further is the people who say these aren’t actually wrong. You see, Lean does focus on reducing waste and speeding up processes while Six Sigma does in fact attack variation and focus on improving quality. The problem is when people stop here.
You see, Lean practitioners are also very concerned with quality and process capability. In fact, it’s virtually impossible to produce product using one-piece flow with an unstable, defect ridden, process. Along the same lines, Six Sigma practitioners also focus on speed and waste reduction. In fact, things like 5S and Value Stream Mapping are now being used by Six Sigma practitioners on a regular basis. Problems arise when we attempt to place either Lean or Six Sigma inside a narrowly defined box.
Continuous Improvement Methodologies
At MAMTC, we prefer to look at Lean and Six Sigma as continuous improvement methodologies that can, and should, be used in harmony with one another.
In our situation, some of us first learned about Six Sigma while working in the private sector, where we used it with great success. We were then introduced to Lean at another company and learned to leverage it in a very successful manner. But, the thing that’s served us the best is having a strong understanding of both Lean and Six Sigma.
Some like to refer to this mixing of Lean and Six Sigma as Lean Six Sigma, while others call it Lean Sigma, or Operational Excellence, or CIP which stands for Continuous Improvement Process. In the end, what it’s called isn’t all that important. As we often say to our clients, it’s not about the names of the tools, but rather about the rules of how and when to apply them.
With this said, there are some unique characteristics to both Lean and Six Sigma. First, while both Lean and Six Sigma are extremely powerful, it’s our opinion that the breadth and depth of the Lean body of knowledge make it better suited as an overall business operating system, while Six Sigma is best leveraged as a problem solving methodology.
Length of Time to Complete a Project
Many companies do use Six Sigma successfully as a way to guide their business on a day-to-day basis. Additionally, Lean projects or initiatives are usually shorter than a Six Sigma project. For example, a typical kaizen event conducted by a Lean practitioner may only last 3 to 5 days while a typical Six Sigma black belt project could last 4 to 7 months.
Again, we run the risk of placing these methodologies into narrow boxes with this sort of explanation, since there are exceptions to all rules. For example, a Lean practitioner may have a large system kaizen project scoped that will take 9 months to complete. But in order to complete it, they’ll conduct many smaller, much faster, point kaizen events.
PDSA vs. DMAIC
Another difference is that Lean practitioners usually use the PDSA, or Plan, Do, Study, Act problem solving methodology to work through an issue, while Six Sigma practitioners typically use DMAIC, or Define, Measure, Analyze, Improve, and Control.
While there are many similarities to these two approaches, the DMAIC method is often a bit more formalized than PDSA. For example, most Six Sigma practitioners must pass a toll gate review in order to move onto the next phase, while PDSA is typically a bit more fluid in nature.
Next, both Lean and Six Sigma practitioners often seek and desire some form of certification. With this said, certification seeking is much more prevalent within the Six Sigma world since the Six Sigma body of knowledge is much tighter.
In fact, much of the Six Sigma body of knowledge can be learned over the course of 2-4 weeks of focused training and then practiced over the course of 6-12 months of project work.
And finally, while both Lean and Six Sigma practitioners leverage the use of statistics to solve problems, it’s common to see Six Sigma practitioners place greater importance on advanced tools such as response surface design of experiments.
With all of this said, you may come across strong proponents of one continuous improvement methodology over the other.
At MAMTC, it’s our opinion that debating which method is better than the other is a genuine waste of time and energy.
Instead, we encourage all continuous improvement practitioners to learn as much as they can about any and all improvement methodologies. In fact, Socrates once said, “To know, is to know that you know nothing. That is the meaning of true knowledge.”