What does Lean Mean in Lean Six Sigma?

"Lean" and "Six Sigma" methodologies seem quite different, but a company can benefit by wisely uniting these approaches.

A Summary of Six Sigma Project Methodology

  • Select projects to maximize financial improvement but define a limited project scope
  • Look at the problem from the customer's point of view
  • Investigate and document the business process, including inputs and outputs
  • Use statistics: take samples and analyze for variations
  • Minimize variations to ensure repeatable quality

A Summary of Lean Project Methodology

  • Minimize inputs and wasted outputs
  • Maximize throughput of any process
  • Start a process to meet the customer's request, rather than to build inventory
  • Produce what the customer requires, correctly, the first time
  • Build "continuous improvement" into every process, by bringing suppliers and front-line workers "into the loop"

Different Methodologies

Based on the above simplified lists, a Six Sigma project would concentrate on analysis and finish by implementing rigid controls. A "Lean" project seems to assume the analysis is complete, since it does not explain how to minimize or maximize. Also, the "Lean" project gives more autonomy to workers, at least to make suggestions for improvements.

Non-Blended Projects

The most obvious approach is to avoid blending these methodologies. "Simply"…and that is a loaded word…use the approach most suited to the problem at hand.  The article, "Choose a Six Sigma Project", shows how to compare projects in order to determine which is the best match for the Six Sigma methodology.

Other projects could fit better with Lean techniques. It may already be obvious that a process has significant waste, or that a "finished goods" warehouse is bulging with inventory.

If the company has separate "centres of excellence" for Six Sigma and Lean practitioners, projects might be selected separately also. The department manager might propose a project to one group or the other, based on that manager's understanding of which is more suitable.

The company could, however, consolidate the decision-making process into one department. That puts the onus for deciding the methodology into one place, and ensures that all candidate projects are evaluated for their potential gains.

Blending the Methodologies: Making Six Sigma "Leaner"

It is rare to add Six Sigma principles to a Lean-oriented company, at least if the Lean methods have been successful. Too often the Six Sigma approach is seen as adding unnecessary delays between the initial selection of projects and the data-gathering phase. Those companies succeed with Lean because their employees already understand their processes and problems well enough to act relatively quickly and correctly.

What would it mean, then, to make a "Leaner" Six Sigma methodology?

The basic concept is to add Lean's "continual improvement" as an ongoing activity to the completion of every Six Sigma project. In this way, Six Sigma moves away from a "project that was completed" to a "process that is ongoing". Continue to gather data to feed Six Sigma's statistical analysis. Continue to seek incremental improvement by empowering the front-line workers to make their suggestions.

Using the Lean "continuous improvement" approach, workers can make changes. Ongoing statistical monitoring provides the data Six Sigma needs to evaluate the success of these changes. If necessary, a new Six Sigma project might be initiated to address new problems or opportunities.

Other definitions

Michael George (1) defines the principles of Lean Six Sigma as:

The activities that causes the customer's critical-to-quality issues and create the longest time delays in any process offer the greatest opportunity for improvement in cost, quality, capital and lead time

Bill Carreira (2) on the other hand defines the concept as

Lean Six Sigma is about relentless, sustained improvement – analysis after analysis, metric after metric, and project after project- lean causes products to move through processes faster, and Six Sigma improves quality.

By Oskar Olofsson