What Six Sigma is
Six Sigma is a process-improvement methodology focused on reducing variability and defects using statistical analysis. It was developed by Motorola in the 1980s and popularized by General Electric, with a strong emphasis on data-driven decisions, unlike Lean, which grew out of a focus on flow and waste elimination.
What a "sigma level" means
Sigma (σ) is a statistical measure of standard deviation, used to express how far a process is from perfection. A "Six Sigma" process produces at most 3.4 defects per million opportunities — an extremely high quality level compared to most industrial processes, which typically run between 3 and 4 sigma.
The DMAIC cycle
Six Sigma projects follow a five-phase structure known by the acronym DMAIC:
Define
Scope the problem, the project boundaries, and the voice of the customer — what actually matters to whoever receives the product.
Measure
Collect reliable data on current process performance, validating the measurement system itself.
Analyze
Identify root causes of variation using statistical tools, not just opinion.
Improve
Test and implement solutions that directly address the root causes found.
Control
Standardize the improvement and monitor the process to make sure the gain holds over time.
Without data, all you have is opinion — and opinion doesn't fix process variability.
Lean Six Sigma: combining both approaches
Many companies combine the two methodologies under the name Lean Six Sigma: Lean attacks speed and waste (flow), while Six Sigma attacks variability and defects (statistics). Together, they cover both "is the process fast enough?" and "is the process consistent enough?" — two questions neither methodology fully answers on its own.
Want to see how Lean and Six Sigma combine in practice?
Download the "Lean & Six Sigma — Transform Your Company's Performance" e-book.
Download the e-book
About the author
Lean Manufacturing & Behavioral Management Specialist
Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.