I regularly see posts and discussion points asking what are the differences between Lean and Six Sigma, should Lean or Six Sigma be used first, and if Lean is better than Six Sigma. I find it really puzzling that people involved in continuous improvement still have this debate, especially since the two techniques are not alternative approaches, but are complementary techniques.
Let’s take a quick look at these three questions
- What are the differences between Lean and Six Sigma?
Lean is the practical application of the Toyota Production System. Lean started out as a simple way to ensure that business were focused on the things that customers value and ensuring the activities in the business are as efficient as possible at delivering customer value. Lean focuses on process velocity, reducing waste in all forms and eliminating non value added activities. There is a bias to immediate action Lean, to ensure that waste is removed in the shortest possible time.
Six Sigma was developed by Motorola to enable effective competition against high quality imports from Japan. Six Sigma is a highly structured process aimed at understanding and reducing variation to ensure that the process always delivers the product or service required by the customer. Six Sigma requires statistical evidence and proof of performance, with a mantra of show me the evidence, the ultimate aim of which is to ensure the product delivered is absolutely consistent and within specification. Six Sigma has a bias to understanding the customer and only acting on statistically valid evidence.
The aim of both Lean and Six Sigma is to reduce waste, particularly defects, improve process performance and thereby increase customer satisfaction. Lean aims to achieve this by identifying and removing waste and non-value added activities. Six Sigma aims to achieve this by ensuring the customer needs are fully understood and the process is capable of delivering the required product consistently.
- Which Should be used first, Lean or Six Sigma
My perception is that if a practitioner is more comfortable with Lean they will use the lean tools first and if they are more comfortable with Six Sigma they will apply Six Sigma first. Let’s phrase that question differently and see if it still makes sense.
Do you want to reduce waste, defects, and lead time for your process through Lean, or do you want to reduce waste, defects and lead time for your process through Six Sigma? I believe almost every production manager and senior executive would ask one more question; why do I have to choose?
Lean and Six Sigma processes are valuable and there is a strong crossover in the skills. For example if final checking of a process is unnecessarily complicated and yielding too many defects, would you want to be certain that the test method was correctly identifying defects? Of course, therefore we should use Six Sigma first right, because that is where we find Gauge reproducibility and repeatability tools? However, would you want to eat until that was done before simplifying the process? If we give in to the tyranny of “or” we have to choose. What if we choose and instead, and use different groups in the team for both exercises. We need to make sure they communicate effectively, but if the tasks are perceived as of equal importance and we promote a collaborative approach, we can get both done in parallel. That way we eliminate the non-value added steps and ensure that we can separate good parts from bad parts.
If we start with Lean we end up with a simple process (good) without knowing if our output performance is due to the test method, operator or parts (bad). If we start with Six Sigma, we know where the variation finished part performance comes from (good), but the process is still very complicated and we still can’t clearly see what needs to change (bad). If we apply both techniques in parallel we get a simplified process (good) with clarity of process performance (good). Applying both in parallel gives the best results.
- Is Lean better than Six Sigma?
Is your car engine more important than the steering? Neither works well without the other, having a car that can go fast, but is hard to direct is not going to work, equally having an excellent capability to direct the car, but nothing to make it move is also going to fail.
Lean and Six Sigma are complementary and whilst each is an excellent tool in it’s own right, when used together these two tools yield results far in excess of what each can give alone. Neither is better than the other, they are different and they are complimentary. Lean or six sigma is not a binary choice, it is a comprehensive toolkit for solving problems.
Just as an engineer uses different tools and techniques for different structures, so Lean and Six Sigma should be applied when the tools and techniques are appropriate to the task in hand.
So my final message on this would be don’t worry about whether the improvement process should be lean or six sigma, instead worry about whether the tool selected to improve the process will yield the most effective solution. In other words don’t get trapped by the tyranny of “or” instead be empowered by the freedom of “and”.