Difference Between Six Sigma and Lean

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Apr 15, 2024

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20 mins

The team must operate in a highly conducive and collaborative atmosphere to achieve success in any project. The project manager is the key person who must drive the project with a highly pressurized environment by motivating the team and he is the bridge between many stakeholders of the projects such as customers, the team, the project board, and the project sponsor, etc. Many industries now prefer highly knowledgeable project managers, having impressive project management background, talent, skills, passion, and certified with one of the project management approaches with the knowledge of multiple key project management frameworks.

There are a lot of project management methodologies such as Prince2, PMBOK, Agile, Lean, XPM, Scrum, and Six Sigma. Choosing the one which applies to your project and your organization requires expertise in them, previous experience, and expert guidance. They produce a lot of benefits such as reduce the defects, reduce variations in the processes, reduce cost and wastes, increase in productivity, faster delivery time to market, increase in profits, defined scope, high quality, enhance process capability, enhance processes performance and standardization of the process in minimum. In this article, we will see the two important frameworks namely Lean and Six sigma.    

What is Six Sigma?

Six sigma is a framework for reducing defects in the services or products and reduce variations in the processes by using the statistical method. Six sigma uses the data-driven and mathematical functions such as the probability analysis, regression analysis, range, mode, mean, median, process capability ratio(Cp), process capability index (Cpk), standard deviation and performance parameters such as Pp and Ppk using various distributions such as normal distributions. The six sigma contains two phases such as DMAIC which is Define, Measure, Analyze, Improve and Control, and Design for six sigma (DFSS) which is also known as DMADV – Define, Measure, Analyze, Design and Verify. All these are used in six sigma to calculate the DPMO that is Defects Per Million Opportunities. For example, using 1 sigma the rate of DPMO is 691,462 and yield is 31%. It increases to 3.4 DPMO and yield is 99.99966 when the process achieves six sigma. It is represented in the chart below.

DPMO in Six Sigma

Benefits of Using Six Sigma 

  • Improved customer satisfaction
  • Improved cycle time
  • Process capability enhancements
  • Process performance enhancements
  • Reduction in defects
  • Reduction in costs
  • Reduction in process variations
  • Set performance goals for the team
  • Employee motivation
  • Distinct roles and responsibilities for the team members
  • Enhanced strategic planning
  • Improved supply chain management etc

What is a Lean Methodology? 

Lean methodology is used to reduce or eliminate wastes in the organization. There are eight types of wastes they are as follow,

  • Waiting time
  • Transportation
  • Overproduction
  • Non-utilized talents
  • Motion
  • Inventory
  • Extra or over-processing
  • Defects

Lean helps in reducing all these waste listed above by properly addressing each one of them with the help of lean tools. There are 5 principles of lean to reduce the waste in the organization, they are as follows,

  1. Value defining and adding
  2. Value stream mapping 
  3. Creation of flow
  4. Using the pull system
  5. Enhancing to the perfection

1. Value defining and adding - The value is what the customer is expecting out of the project that is, deliverables. To add value is improving and adding new features or enhancement to the products from one process to another. We must know what value is according to the customer is and focus on that and eliminate all non-value-added waste in the process and the waste features in the products or services.

2. Value stream mapping - Here from the first step we need to add only the features that add value. 2 types of waste are non-value-add but necessary and non-value, non-necessary. The later one must be eliminated and the first one must be reduced as much as possible.

3. Creation of flow - The flow of the products from the first process to the next must be smooth without any delays. All the value-added activities must flow uniformly without any interruptions one after another till the completion of the services or products.

4. Using the pull system - This is the name of the concept called Just-In-Time mechanism or Kanban system where there is no overproduction or less production and no waiting time. The goods are produced based on the pull experienced by the subsequent station or the processes. The inventory is the biggest waste: instead of stocking everything based on the pull, the right amount of inventory is replenished.

5. Enhancing to perfection - This is based on the Kaizen system which says "Make small improvement every day". All the employees must strive for perfection in the process and make small improvements in the systems on each passing day. This leads to the organization which is striving towards perfection and learning every day.

Why use Lean? 

The lean methodology has many benefits and those are listed below,

  • Managing the team and process complexities in an improved way
  • Changing priorities are managed in a better way
  • Make the business process efficient
  • Project visibility is enhanced at the team level
  • Reduced lead time
  • Increase in productivity at the organizational level
  • Enhancement of visibility to stakeholders
  • Reduction in costs
  • Team motivation is increased
  • Deliver the customer value in a predictable way

Tabulate - Difference between six sigma and lean

Lean Vs Six Sigma
Serial #
Six Sigma
1DefinitionReduce waste in the organization and processesIt is a methodology for reducing the defects in the processes and reducing the variations in the process
2MethodBased on eliminating 8 wastes in the organizationBased on the statistical methods to enhance the quality of the products or services and to improve the processes
3PrinciplesBased on 5 principles of leanBased on the 2 methods DMAIC and DMADV (DFSS)
4ToolsKaizen, Kanban, the 5S, PokeYoke, etcBased on the regression analysis, probability theories, 5 Why’s,  range,  median, mode, mean, Cp, Cpk, Pp, Ppk, standard deviation, etc.
5MeasuresCycle time and Inventory turnsDefects Per Million Opportunities (DPMO)
6Major Benefits

• Value addition

• Profitability

• Customer satisfaction

• Zero waste

• Profitability

• Customer satisfaction

• CTQ (Critical To Quality)

• CTC (Critical To Customer)

7ApplicationAll the processesAll the processes

Conclusion –Six Sigma Vs Lean, Which is better, and why? 

We have seen both the Lean methodology and the six sigma methodology’s use in different circumstances. Both are having different benefits and are completely different interests in the organization. One must decide which one you need the most and will be beneficial in your particular projects. But there is something called an integrated project management system wherein you can apply both the project management methodologies together. One will complement the other so there are no issues in applying both the methodologies.

As you have a brief understanding of both the frameworks, we recommend that you choose the Certification you want and attend online interactive Green Belt training with the StarAgile training institute. To explore more and register click on the appropriate link provided in this blog.


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