Six Sigma and Lean Six Sigma are two process improvement methodologies for enhancing operational performance. While often mentioned together, they represent distinct approaches to achieving greater efficiency and quality. Understanding the focus of each is important for organizations to determine which framework best aligns with their particular goals.
What Is Six Sigma?
Six Sigma is a data-driven methodology focused on eliminating defects and reducing process variation. Its objective is to achieve a performance level of fewer than 3.4 defects per million opportunities, a 99.99966% defect-free rate. This statistical target is where the name “Six Sigma” originates, referring to six standard deviations between the process mean and the nearest specification limit.
Originating with Motorola in the 1980s, it was developed to improve manufacturing quality by systematically measuring and eliminating defects. At its core, Six Sigma uses a structured problem-solving framework known as DMAIC: Define, Measure, Analyze, Improve, and Control.
In the Define phase, the problem and goals are established. The Measure phase involves collecting data on current performance. During the Analyze phase, statistical analysis identifies the root causes of defects. The Improve phase focuses on implementing solutions, and the Control phase ensures improvements are sustained.
What Is the Lean Methodology?
The Lean methodology focuses on maximizing customer value while minimizing waste. Its goal is to improve process flow and efficiency by removing any step that does not add value from the customer’s perspective. Originally part of the Toyota Production System, Lean principles are now applied across many industries to streamline operations.
Lean defines waste as anything that consumes resources without creating value. The methodology identifies eight types of waste, remembered by the acronym TIMWOODS:
- Transportation (unnecessary movement of products)
- Inventory (excess products and materials)
- Motion (unnecessary movement by people)
- Waiting (time spent idle)
- Overproduction (producing more than needed)
- Over-processing (doing more work than required)
- Defects (products or services out of specification)
- Skills (non-utilized talent of employees)
By targeting these areas, organizations can achieve improvements in speed and resource utilization.
Understanding Lean Six Sigma
Lean Six Sigma is a hybrid methodology that integrates Lean’s emphasis on speed and waste elimination with Six Sigma’s focus on quality and defect reduction. This combined approach allows organizations to make processes more efficient and precise, resulting in an operation that is faster and delivers higher quality.
This methodology uses the structured DMAIC framework from Six Sigma as its problem-solving backbone. It expands the toolkit by incorporating Lean principles to identify and remove non-value-added activities throughout each phase. For instance, when analyzing a process, a team would use statistical tools to find causes of variation and Lean tools like Value Stream Mapping to eliminate bottlenecks and delays.
The two methodologies are complementary. Lean principles enable a process to run faster by removing wasteful steps, which can expose underlying quality problems. The statistical rigor of Six Sigma ensures that changes made to improve speed do not inadvertently introduce new errors or increase process variability.
Key Differences Between Six Sigma and Lean Six Sigma
While Six Sigma and Lean Six Sigma share the goal of process improvement, their focus and tools differ. Six Sigma is concerned with reducing process variation and eliminating defects, making its approach problem-focused on a specific issue where quality does not meet the standard.
Lean Six Sigma, in contrast, has a broader goal. It aims to eliminate waste in all its forms while also reducing defects, giving it a holistic focus on the entire process flow, or value stream.
This difference in focus is reflected in the tools each methodology employs. Six Sigma relies on statistical analysis, control charts, and the DMAIC framework to solve problems. Lean Six Sigma uses this same DMAIC structure but integrates a wider array of tools from the Lean toolkit, such as Value Stream Mapping, 5S, and Kaizen events. The impact of Six Sigma is improved quality and consistency, whereas Lean Six Sigma delivers improvements in quality, speed, and efficiency.
How to Choose the Right Approach
The decision between Six Sigma and Lean Six Sigma hinges on whether the primary issue is related to defects or a combination of waste and defects.
A company might choose Six Sigma when confronted with a complex quality control issue that has a high defect rate in a specific part of its operation. For example, if a manufacturing line is producing a component with inconsistent dimensions that lead to product failures, Six Sigma’s statistical tools and DMAIC approach would be suited to identify and control the sources of that variation.
An organization would opt for Lean Six Sigma when it needs to improve an entire process to make it faster, more efficient, and more accurate. Consider a financial institution’s mortgage approval process that is slow, involves redundant paperwork, and results in data entry errors. A Lean Six Sigma project would use Lean tools to map the workflow, eliminate unnecessary steps, and apply Six Sigma methods to reduce the error rate, improving both speed and quality.