Comparing Lean and Six Sigma

Comparison between Lean and Six Sigma reveals that Lean is a philosophy of identifying and eliminating non-essential and non-value adding activities to streamline production and thereby improve quality, whereas Six Sigma is a change management methodology to manage, improve, and or reinvent business processes to limit process variations to 3.4 defects per million opportunities and thereby improve quality.

The fundamental difference between Lean and Six Sigma is that “Lean” is a philosophy and Six Sigma is a program. Lean attempts to inculcate an organizational culture change and permanent behavior change among employees, to identify and eliminate waste, whereas Six Sigma is a methodological process intervention that does not attempt to change the organizational culture or attempt a permanent behavioral change among employees.

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"Lean" identifies the need for a process or activity first and if the activity adds value tries to improve on such activity through improved process flow and enhancing productivity. Six Sigma focuses specifically on eliminating process variations in output without looking into the merits of such processes in the scheme of things.

Lean, as the name suggests breaks down processes to bare bone essentials under its guiding principle that any activity or function that does not add value constitutes waste that needs elimination.

Six Sigma, on the other hand does not question whether the activity or function adds value and works under the guiding principle that any variation in existing process or output is waste.

Lean is continuous and on-going approach, under the assumption that the day-to-day changes in technology, external environment and other factors always leave room for improvement. Six Sigma, on the other hand is a project-based approach, and the Six Sigma project group disbands on achieving the set change objectives, leaving metrics or control charts to prevent roll back.

A major difference between Lean and Six Sigma pertains to the ownership of the concepts.

Lean aims at continuous improvement across the entire value-stream of operations by encouraging and empowering the entire workforce to identify and eliminate waste in their sphere of activity. It is an on-going process ingrained to operations of the firm, and requires adoption by the entire workforce and in all aspects of the company operations for effectiveness.

Six Sigma, on the other hand is a methodical approach that aims to eliminate variations in a specific project or area of operations, and the results remain confined to such specific area instead of permeating to the entire organization. The onus on implementation of Six Sigma falls on special purpose teams such as inventory reduction team, manufacturing scrap reduction team and others formed specifically for the purpose. Such teams have Green Belts led by a Black Belt or Master Black Belt, who remain exclusively responsible for the implementation of Six Sigma. The Six Sigma team may choose to involve other sin the implementation part at their discretion.

Lean works by transferring knowledge and implementing the culture of a learning organization across the board to bring about changes in business strategy, structure, and processes. The implementation of lean is through tools such as Value Stream Mapping, Five S, Kanban, and poka-yoke or error-proofing, and through concepts such as Just in time manufacturing.

The implementation of Six Sigma is through the DMAIC (Define, Measure, Analyze, Implement, and Control) or DMADV (Design, Measure, Analyze, Design, Verify) procedure and using tools such as Failure Mode Effective Analysis (FMEA) and Analysis of Variance (ANOVA). The Six Sigma team identifies root causes for variance, test hypotheses for possible solutions, and validate the analysis, before implementing the solution and monitoring for effectiveness.

Both Lean and Six Sigma have their uses and very often go hand in hand. While Six Sigma remains more eared to solving pressing customer needs, Six Sigma alone cannot improve overall process speed or maximize returns on investment for investors.

Lean Six Sigma (LSS) tries to combine the advantages of these two approaches and minimize the weakness of both. The Lean Six Sigma methodology entails using lean methodologies to identify and remove non-value adding activities and processes, and then applying Six Sigma methodologies to identify and eliminate process variation.

The tools used for the implementation of Lean and Six Sigma often overlap. 5S, for instance while a common Lean tool also finds uses in the Control phase of a Six Sigma DMAIC project.

In comparison, Lean and Six Sigma suggest that while fundamental differences distinguish these two concepts, they nevertheless remain complimentary.