Lean or Six Sigma:
Which Should I Use?

For many companies looking to engage in continuous improvement activities, this can be a daunting question. The answer to the question (and I’m sure you guessed it) is a resounding: IT DEPENDS!

More precisely, it depends on the goals the company and the areas in which it wants to improve. For nearly all companies, improvement opportunities can be summarized into three key areas: cycle time, cost, and quality.

When we consider the use of Lean and Six Sigma methodologies to make improvements in these areas, they are distinctly different – but complementary. In other words, it is imperative that the correct methodology be employed in order to achieve the desired goal.

Let’s take a closer look at the characteristics of Lean and Six Sigma and see how these methodologies align with these improvement opportunities. Lean is about eliminating waste (non-value-added activities), standardizing work processes, and achieving “flow”. By eliminating unnecessary tasks, it is logical to assume it will take less time and resources to complete the finished product. Consequently, the key benefit in the application of Lean is a reduction in cycle time.

By their very nature, Lean projects possess characteristics that tend to be process-based. Typically, emphasis is placed on examining value streams and work processes, as opposed to focusing on individual products. The Lean tool set provides rigor in assessing the activities of the product (the “thing” going through the process*), the operator, and even the machines (if applicable) employed by the process. Through successful adaptation of these tools, improvement in the overall process can be achieved.

Six Sigma is focused on variation reduction and process control. The Six Sigma approach is based on a simple premise: that in order to achieve a consistent and predictable output, it is necessary to control the inputs. Often, this statement is expressed as the mathematical expression: y=f(x).

The Six Sigma methodology employs a suite of statistical tools to understand the degree, as well as the sources, of variation. Projects under the Six Sigma umbrella tend to be product-based. For example, a product with a high scrap rate would employ Six Sigma tools to identify the contributing factors that cause the non-conformities. Once a solution had been identified and implemented, Six Sigma tools would also be used insure the process was consistent in maintaining the improved level of performance.

The fuel that makes the Six Sigma engine go is data. Access, and the analysis of data, is the key for successful utilization of a Six Sigma program - and a Design for Six Sigma (DFSS) program for that matter – as well. The ability to identify and analyze the causes of variation is the key to the Six Sigma approach. Consequently, the key benefit in the application of Six Sigma is a reduction in quality defects.

It is important to recognize, that although we highlighted benefits related to cycle time and quality in our review of Lean and Six Sigma, cost is not forgotten. Significant cost benefits can be realized from the application of both Lean and Six Sigma. For example, for a Lean project, cost benefits can be realized from reduced labor and resources required to produce a product. Likewise, reduced scrap rates and higher product yields from a Six Sigma project would translate into significant cost savings as well.

It is also important to note that the benefits highlighted for Lean and Six Sigma are not mutually exclusive. For example, the ability to standardize a work process in a Lean project provides the byproduct of reducing the variation that exists in the process. In the Six Sigma world, the ability to eliminate a chronic rework cycle, for example, would certainly improve the cycle time for producing the product.

Many companies that utilize both Lean and Six Sigma methodologies have adopted the term “LeanSigma” and formally applied it in the naming of their continuous improvement organizations. Regardless of the organizational structure, the bottom line is this: The companies that understand the fundamental differences in Lean and Six Sigma, and understand the complementary nature of these methodologies in achieving benefits related to cycle time, cost, and quality, are the ones who will benefit the most from its implementation.