Lean vs. Lean Six Sigma: Which Path is Better for You?

In a world where efficiency, quality and customer satisfaction are paramount, professionals across sectors are turning to process improvement methodologies to stay competitive. Two of the most popular approaches are Lean and Lean Six Sigma. Both methodologies aim to streamline operations, improve quality and eliminate waste, but they do so in different ways and with different tools.

If you're looking to upskill, lead change or simply make your work more effective, you might be wondering: Should I study Lean or Lean Six Sigma? Hopefully, this article will help you understand the core principles of each, explore their similarities & differences, and guide you in choosing the best path according to your goals.

Lean is a methodology rooted in the Toyota Production System (TPS), developed in the 1940s. The Toyota Production System is a manufacturing system with the objective to completely eliminate waste and shorten lead time, therefore delivering vehicles to customers quickly, at a low cost and with high quality (source: Toyota).

The TPS is based on two pillars:

1. Jidoka

• Jidoka is described as “automation with a human touch” where machines are designed to detect abnormalities, for example equipment malfunctions, quality issues or delays, and stop automatically, or allow operators to halt production manually.
• This prevents defective products from progressing and enables quality to be built into the process.
• To develop such intelligent automation, work must first be perfected manually, with kaizen (continuous improvement) applied to eliminate waste (muda), inconsistency (mura), and overburden (muri).
• Once the process is stable and efficient, it can be mechanized with built-in abnormality detection, resulting in a production line that is high-quality, cost-effective, flexible, and easy to maintain.

2. Just In Time

• Just-In-Time (JIT) is about producing only what's needed, when it's needed, and in the quantity needed.
• A car is made up of over 30,000 parts, and those parts are produced by both Toyota and other manufacturers.
• To avoid delays in car production, the minimum number of parts are kept in stock for the assembly line to build car as soon as an order is received. If you waited for an order to be received before ordering the parts, the car would not be built for months – not what the customer expects!

The primary focus of Lean is on eliminating waste (known as muda in Japanese) and creating more value for customers using fewer resources.

There are 5 core Lean principles:

1. Value – Define what is valuable from the customer’s perspective.
2. Value Stream – Map all steps in the process and identify non-value-adding activities.
3. Flow – Ensure that processes flow smoothly without interruptions.
4. Pull – Produce only what is needed, when it is needed.
5. Perfection – Continuously improve processes to strive for perfection.

There are some common tools available. These can be used to help organisations deliver continuous improvement through improving efficiency, reducing waste and managing workflows. I have listed four of the most common lean tools below:

• Value Stream Mapping (VSM) – a visual flowchart to document, analyse and improve the end-to-end process needed to deliver a product or service.
• 5S (Sort, Set in order, Shine, Standardize, Sustain) – a 5-step method for keeping the workplace in good order.
• Kanban (Visual workflow management) - a visual tool to help teams visualise and manage their work.
• Root Cause Analysis (e.g., 5 Whys) – a technique used to explore the root cause of a problem.

Lean is not restricted to be used in just the automotive industry or where production lines are used. It is also widely used in healthcare, logistics, and increasingly in service industries. It’s especially effective in environments where speed, flexibility, and customer responsiveness are key.

Six Sigma is a data-driven methodology formally developed by Motorola in the 1980s. It is used to improve business processes by identifying and eliminating variation in the process, resulting in enhanced quality, performance and customer satisfaction. 

Motorola first started using Six Sigma to standardise defect measurement and to improve manufacturing performance, which reduced the likelihood that an error or defect will occur. Six Sigma aims for near perfection and was used by Motorola as a performance metric; specifically defining no more than 3.4 defects per million units.

Sigma is a statistical term that measures process variation.

The primary focus of Six Sigma is to reduce variation and defects through data-driven process improvement.

Core Principles

Six Sigma follows a structured problem-solving approach, using statistical tools, to improve existing processes or to design brand new processes. 

The approach for improving existing processes is called DMAIC:

• Define the problem and customer requirements
• Measure current performance
• Analyze root causes of defects
• Improve the process
• Control the improved process to sustain gains

The approach for designing new processes or products, using Six Sigma is called DMADV:

• Define – define the project or process
• Measure – determine customer requirements
• Analyze – identify functions. Generate & select concepts
• Design – develop a design and test/optimise the design components
• Verify – confirm that design works as intended, and implement the design

As with Lean, there are also common Six Sigma tools available. These provide organisations with a structured and data-driven approach to improving process, reducing waste and enhancing quality:

• Statistical Process Control (SPC) - a statistical technique to monitor and control a process.
• Process Capability Analysis - determines how well a process can produce outputs that meet specifications or customer requirements.
• Fishbone Diagrams – a visual tool used to systematically identify and analyze the root causes of a specific problem.
• Hypothesis Testing - a statistical method used to make decisions or inferences based on sample data.
• Control Charts - monitor how a process changes over time.

Again, Six Sigma is not constrained to a particular industry. Six Sigma is particularly valuable in environments where precision, compliance, and consistency are critical, for example pharmaceuticals, finance, and manufacturing.

As you would expect, there are similarities between the two with the obvious overlap of Lean in both approaches. Below is a summary of the similarities between Lean and Lean Six Sigma:

• Both aim to improve processes and deliver better value to customers.
• Both encourage a culture of continuous improvement.
• Both use structured approaches and tools to solve problems.
• Both can be applied across a range of industries and functions.

Below is a guide to help you decide when to choose Lean vs. Lean Six Sigma, based on your goals, challenges, and resources:

Many organizations combine both approaches into Lean Six Sigma, leveraging Lean’s speed and flow improvements with Six Sigma’s precision and quality control.

Pros and Cons

There are pros and cons to both Lean and Lean Six Sigma approaches, please see below for a summary of these:

Lean Pros:

• Easier to adopt with less training
• Quick wins and visible improvements
• Strong focus on culture and employee engagement

Lean Cons:

• May not address variation in the process
• Less emphasis on data and measurement

Lean Six Sigma Pros:

• Comprehensive and balanced
• Combines speed with precision
• Widely recognized and respected certification

Lean Six Sigma Cons:

• Can be overwhelming for beginners
• Requires commitment to both cultural and technical change

Choosing between Lean and Lean Six Sigma depends on your career goals, industry, job role and organisational requirements. Here are some questions you should answer to help guide your final decision:

1. What are your career aspirations?

• If you're aiming for roles in operations, quality, or continuous improvement, Lean Six Sigma (especially at Green or Black Belt level) can be a strong differentiator.
• If you're looking to enhance team performance or lead agile, customer-focused projects, Lean may be more immediately applicable.

2. What kind of problems are you solving?

• If your challenges involve waste, delays or inefficiencies, Lean tools can help you make quick improvements.
• If you're dealing with defects, compliance issues or process variation, Six Sigma’s statistical approach may be more effective.

3. What is your organisation’s maturity level?

• If your organisation is just starting its improvement journey, Lean can be a great entry point.
• If your organisation already has a culture of data-driven decision-making, Lean Six Sigma may be a natural next step.

4. How much time and training are you ready/able to invest?

• Lean training is often shorter and more accessible.
• Lean Six Sigma certifications (especially Green and Black Belt) require more time, study, and often a project to complete.

Both Lean and Lean Six Sigma offer powerful frameworks for improving processes, delivering value and driving positive change. The right choice depends on your goals, your context and your appetite for learning.

• Lean is ideal if you want to start small, focus on culture, and make fast, visible improvements.
• Lean Six Sigma gives you the best of both worlds; combining speed with rigour, and culture with analytics.

Whichever path you choose, investing in continuous improvement skills is a smart move for any professional. These methodologies not only enhance your ability to solve problems, they also position you as a leader in driving meaningful, lasting change.