What is Six Sigma and how does it work?

six sigma

What is Six Sigma? You must have heard about six sigma many times. This blog will help you to understand the six sigma principle, the practical benefits, the methodology of six sigma, and how to implement six sigma in your business.

  1. What is six sigma?
  2. Benefits of Six Sigma
  3. What is DMAIC (Define-Measure-Analyze-Improve-Control) method?

What is six sigma?

Six sigma is a statistical technique utilized to measure variability in the manufacturing/business process and improve the process by eliminating process variability. Six sigma helps to identify causes of the quality issues/defects in the manufacturing/business process. Six Sigma tool helps to minimize / causes of defects in the manufacturing process.

The following diagram helps to understand the principle of six sigma. Every process output produces a bell-shaped curve. This bell-shaped curve divides into two symmetrical sections. An ideal manufacturing/business process generates a normally distributed curve. If your manufacturing/business process generating a normally distributed curve, it means your manufacturing/business process is in control. If your manufacturing/business process does not generate a normally distributed curve, it means it’s time to take action to improve the business process.

What is six sigma? Six sigma is a statistical technique utilized to measure variability in the manufacturing/business process and improve the process by eliminating process variability. Six sigma helps to identify causes of the quality issues/defects in the manufacturing/business process. Six Sigma tool helps to minimize / causes of defects in the manufacturing process.

The 6sigma principle is very simple, it indicates whether the process output is normally distributed and process variation falls within +/- 3 Sigma from the mean value or not. That’s how total variation is calculated from -3 Sigma to +3 Sigma.

Benefits of six sigma?

What are the benefits of six sigma?

1.Six Sigma tool helps to reduce process and product cost.
2.It helps to reduce lead time in the business process or the supply chain.
3.It helps to build a good manufacturing/business process eventually it helps to achieve better customer satisfaction.
4.Six Sigma tool is not just limited to improving existing / already implemented business/ manufacturing process, it is very useful to design a new business/manufacturing process.
5.It’s a very useful tool for project management.
6.Six Sigma tool helps to identify variation in the process and it helps to minimize the same. 
7.It helps to improve the product/process quality.
8.It helps to minimize or eliminate waste in the process.
9.Six Sigma tool not just limited to can be implemented in any industry.

How many types of Six Sigma are there?

There are mainly two types of six sigma methodology used,
1. DMAIC (Define-Measure-Analyze-Improve-Control)
2. DFSS (Design for Six Sigma)
DMAIC is suitable for process improvement. DFSS is used for designing a new business process.

Let’s understand each six sigma methodology in detail,

DMAIC (Define-Measure-Analyze-Improve-Control)

DMAIC consists of 5 steps, 

  1. Define
  2. Measure
  3. Analyze
  4. Improve
  5. Control

Define Phase

Following the six sigma define-phase charter helps to understand about define phase elements.

What is six sigma?
How six sigma works?
Six-Sigma Define Phase

Following key elements/content helps to define the six sigma project scope, objective, team members, sponsor, timeline.

  1. Define business case/problem statement: It’s the first step of six sigma to define the problem statement. Problem system can be poor product quality, delay in service, poor sales, damage in goods transportation, customer complaints, increased number of accidents in the manufacturing set-up. A problem statement should be defined in the proper way for better success and results. A clear problem statement helps to define SMART goals. The hypothetical problem statement leads to six sigma project failure.

Use 5-Why & 1H technique to define the problem statement. The following questions can help you to refine the problem statement.

  • What went wrong?
  • Where the problem/defect observed?
  • When the problem recorded/observed?
  • Who reported the problem/defect?
  • Why defect/problem not detected within the organization.
  • How defect/problem could be avoided?
  1. Project scope & goal: Based on the problem statement define SMART goal,


M-Measurable (practical)


R-Realistic / Relevant

T-Time bound

It’s a very important step in the define phase, project scoping is essential to execute the six sigma project effectively. Project scope and goal helps to decide whether six sigma green belt or six sigma black belt project to be executed.

Cost Saving: Remember six sigma tool/technique is not just limited to quality improvement. Six Sigma tool can also help to save operational/manufacturing cost. Saving can be achieved in various streams.

1.Saving in production cost 

2.Saving in material cost

3.Saving by eliminating defects/cost of poor quality.

4.Saving by eliminating waste (Muda-Mura-Muri) in the operation /manufacturing process.

  • Muda- Waste
  • Mura- Overburden
  • Muri- Unevenness

Saving can be hard saving or soft saving. 

Examples of hard savings are reduction in travel cost, reduction in raw material cost.

Examples of soft savings are increased customer satisfaction, elimination of defects/cost of poor quality.

  1. Project Expenses / Investment: Every six sigma project needs little or significant investment. Investment may require for installation of ERP or enhancement in existing ERP or installation of advanced technology/machines. The investment must be reviewed carefully and management commitment required for project funding.
  2. Project Sponsor: The project sponsor allocates sufficient/estimated funds for the six sigma project execution.
  3. Project Leader: The role of the project leader is to keep track of six sigma project expenses, six sigma project timeline. The project lead/leader is accountable for the successful execution of the six sigma project on time. The project lead must be a six sigma black belt certified or green belt certified.
  4. Project Team: Project team member selection must be done wisely. The selection of the project team is mainly depending on the project goal and scope. Project team members should be trained on six sigma fundamentals.
  5. Subject Matter Expert: Subject matter expert selection mainly depends on the project scope.
  6. Six sigma project schedule: Remember any plan, a project without a schedule just remains as plan on the paper. This statement is also applicable for the six sigma project. The project schedule must be defined for each six sigma DMAIC/DFSS phase.

Measure Phase:

The second phase of the six sigma DMAIC methodology is the ‘measure phase’. The name of this step itself indicates the intent of this phase. In this phase, input parameters, output parameters like defect/non-conformance, delay, and other problems of the business/manufacturing process are measured systematically. Refer to the following image to understanding the six sigma DMAIC methodology ‘measure phase’ quickly.

Consider the following steps to execute the measure phase.

  1. Planning: Develop a plan to complete the measure phase with a defined timeline and roles and responsibilities. Measure phase one of the key critical phase of the six sigma DMAIC phase. If process measurement is not accurate or inconsistent, the next DMAIC phases ‘analyze’, ‘improve’ and ‘control’ will fail. Consider the following elements to build a better plan,

 a. SWOT Analysis: This analysis will help to identify strengths, weaknesses, opportunities, and threats. Remember to keep this SWOT analysis specific to a problem statement and six sigma project scope.

b. Data Collection Plan: Develop a data collection plan with a defined timeline, resource allocation. Refer to the following set of questionnaire to build a data collection plan,

  1. How to collect data? 
  2. Which data collection tool/techniques to be used?
  3. MSA/Gage R&R of measurement tools completed?
  4. How to record and report data? Format types?
  5. Who will collect data? Allocate resource.
  6. Timeline to complete data collection task.

2.Process Map/Process Flow Chart: Define existing business process/manufacturing process graphically. Select appropriate process map type. Following process flow chart/map types can be selected based on the problem statement and six sigma project scope.

  • 1.Swim-lane/cross-functional process map
  • 2. High-level process map (macro)
  • 3. Micro level process map
  • 4. Block diagram
  • 5. Current state process map
  • 6. Future state process map
  • 7. SIPOC
  1. Measurement System Analysis (MSA): MSA is a statistical method used for detecting or determine variations within a measurement system. In MSA; statistical methods like gauge repeatability and reproducibility are used to determine whether a tool/instrument is capable enough for an accurate and precise measurement or not. 

      Eg. If you have to measure lux level (illuminance) in the quality inspection room as per the data collection plan, the first step is to complete the MSA of the lux meter. If lux meter readings are not accurate you will be ending up recording an in-accurate lux level.

  1. Data Collection: Accurate and precise data collection will help to execute the six sigma project successfully. 

Following tools and techniques/questions can help you to collect data accurately,

  1. Focus on the problem statement and project scope and determine which data to be measured? 
  2. List down input & output parameters of the business/manufacturing process. Eg. Lead time of delivering products to a customer. Or turn-around time of addressing customer complaints.
  3. Data collection techniques – There are several ways of collecting data eg. visiting manufacturing site/station and conducting an interview/discussion to understand machine parameters, raw material parameters. Collect last 2-years shop-floor accident trends /logbook. Collect last 3 years machine parameters, history card, and machine maintenance records. Collect last 2 years defects/rejection trends.

Analyze Phase

Once data in the measure phase is collected, the next step is to analyze the data. In this phase, more focus should be on accurate data analysis to complete the root cause analysis of the business problem/problem statement.

The following steps help to complete analyze phase effectively,

  1. Select the right data analysis tool: Several data analysis tools are existing in statistics, you have to select the right tool wisely. It’s the responsibility of the six sigma project lead to guide team members to select an appropriate tool.

          Following data analysis tools can be selected based on the six sigma project scope and problem statement.

  1. Histogram
  2. Scatter diagram
  3. Box Plot
  4. Design of Experiments
  5. Check-sheet
  6. Control Chart
  7. Pareto Analysis
  8. Stratification Diagram
  9. Co-relation study
  10. Hypothesis testing
  11. Regression Analysis
  12. Brainstorming

Conduct the root cause analysis: Several root cause analysis tools can be used eg.

  1. 5 Why Analysis
  2. Ishikawa / Fishbone diagram
  3. Corrective Action & Preventive Action (CAPA)Failure Mode Effect Analysis (FMEA)
  4. Pareto Analysis
  5. A3 Problem Solving tool

Improve Phase:

Once the root cause is identified next step is to discover a corrective action to eliminate a root cause. The following steps help to complete improve phase,

  1. Identify corrective Action: Brainstorming & Benchmarking
  2. Verify & Validate Corrective Action:
  3. Implement Corrective Action:

Following improvement techniques can be considered

  1. Lean Manufacturing: Waste elimination in business/manufacturing process.
  2. 5S or 6S: For better workplace management
  3. Continuous Improvement/Kaizen: For continual improvement in productivity, safety, and quality.
  4. Visual management: For a better and effective way of information and instruction flow
  5. Mistake proofing: To deploy a foolproof system to avoid defect/defective products
  6. Line balancing: To reduce tact time and improve productivity
  7. Training and skillset assessment: To improve operators/staff’s skill, decision-making skills.
  8. Preventive actions: To reduce potential failure mode by initiating a preventive action.
  9. Process/product audit: For better compliance
  10. Process Capability – Cp, Cpk study: To check and review whether a process is stable and capable to deliver expected output.
  11. Just in time: Better response from the supplier/customer and better productivity.
  12. Kanban: For better inventory management

Control phase:

This is the last phase of the six sigma DMAIC methodology. In this phase, a major focus is on sustaining implemented improvement/corrective action. To maintain the effectiveness of corrective/improvement action it’s very important to deploy a process-oriented system instead of the people-oriented system. Following techniques/methodology helps to sustain the effectiveness of improvement actions,

  1. Continual improvement and Quality culture.
  2. Deployment of a statistical process control system for regular monitoring of business/manufacturing processes.
  3. Regular training and employee skill enrichment.
  4. Deployment of mistake-proofing system
  5. Awards and rewards for a process improvement initiative
  6. Deployment of FMEA and control plan
  7. Deployment of SOP/WI
  8. Process/QMS/Product audit 

We hope this blog is useful and helps to clarify the concept of six sigma. Please do share our blog on social media!

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