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What Is Six Sigma? Complete Guide to Its History, Benefits, DMAIC Methodology, Belt Levels, Tools, Applications, Examples and Lean Six Sigma

Six Sigma is a structured, data-driven methodology for improving processes by identifying and eliminating the causes of defects, errors and unwanted variatio...

Bison Technical Team Enterprise IT specialists

Updated 28 Aug 2026 18 min read 0 total views

Six Sigma is a structured, data-driven methodology for improving processes by identifying and eliminating the causes of defects, errors and unwanted variation.

Instead of solving business problems through assumptions, intuition or temporary fixes, Six Sigma emphasizes measurement, data analysis, root-cause identification and controlled improvement.

The American Society for Quality (ASQ) describes Six Sigma as a disciplined quality-improvement approach that helps organizations improve business-process capability by reducing variation that causes defects or errors.

Although Six Sigma originated in manufacturing, it can be applied to almost any measurable process, including:

Manufacturing
Information Technology
Software development
IT support
Banking
Accounting
Healthcare
Logistics
Telecommunications
Customer service
Retail
Insurance
Supply chain
Human resources
Government operations
Education
Sales
Finance
Technical support

The basic philosophy is simple:

Measure the process → understand the problem → identify the root cause → improve the process → control the improved process.

Why Is It Called "Six Sigma"?

The word Sigma comes from statistics.

The Greek letter σ (sigma) represents standard deviation, which measures how much values vary or spread around their average.

Imagine a manufacturing company producing 10-mm components.

If almost every component measures extremely close to 10 mm, the process has low variation.

If components are produced at:

9.2 mm
10.6 mm
9.7 mm
10.8 mm
9.4 mm

the process has considerable variation.

Six Sigma attempts to understand and reduce such variation so that outputs consistently meet customer or engineering requirements.

Therefore, Six Sigma is not simply about checking defective products after production. It focuses heavily on improving the process that creates the product or service.

What Does Six Sigma Quality Mean?

A commonly cited Six Sigma performance target is approximately:

3.4 defects per million opportunities (DPMO).

ASQ identifies 3.4 defects per million opportunities as the numerical goal associated with a process operating at the Six Sigma level.

DPMO stands for:

Defects Per Million Opportunities

For example, suppose a company performs one million transactions.

At a Six Sigma performance level, the commonly used benchmark would correspond to approximately:

3.4 defects per 1,000,000 opportunities.

This represents an extremely high level of process performance.

Sigma Levels Explained

A simplified way of understanding sigma levels is that a higher sigma level generally means fewer defects and a more capable process.

Sigma Level	Approximate Defects per Million Opportunities
1 Sigma	691,462
2 Sigma	308,538
3 Sigma	66,807
4 Sigma	6,210
5 Sigma	233
6 Sigma	3.4

These conventional DPMO values use the commonly taught Six Sigma assumption involving a long-term 1.5-sigma process shift.

The important business concept is:

Higher Sigma Level = Lower Defect Rate

Who Invented Six Sigma?

Six Sigma was developed at Motorola during the 1980s.

Motorola engineer Bill Smith is generally regarded as the principal originator or "father" of Six Sigma. His work focused on the relationship between manufacturing defects, process variation, reliability and failures experienced by customers.

Motorola CEO Robert "Bob" Galvin played a critical leadership role by supporting the methodology and making quality improvement a major corporate priority.

ASQ's historical material identifies Six Sigma as evolving from work performed by Bob Galvin and Bill Smith at Motorola during the 1980s.

Therefore, a useful distinction is:

Bill Smith — principal developer/founder associated with Six Sigma

Bob Galvin — Motorola CEO who strongly championed its organization-wide adoption

Other specialists, including Mikel Harry, subsequently contributed to the development and expansion of Six Sigma methods.

Why Did Motorola Develop Six Sigma?

Motorola faced significant concerns regarding product quality, defects and customer satisfaction.

The organization needed a systematic method of:

Reducing defects
Increasing reliability
Controlling manufacturing variation
Improving customer satisfaction
Reducing the cost of poor quality
Making quality measurable
Improving processes continuously

Motorola therefore began using increasingly rigorous statistical quality-management techniques.

ASQ's historical account notes that Motorola's Six Sigma initiative arose in response to declining product quality and increasing customer dissatisfaction.

Motorola's initial Six Sigma system was deployed in 1987, before the extensive belt-based training infrastructure associated with modern Six Sigma became common.

How Did Six Sigma Become Popular Worldwide?

Motorola created the foundation, but Six Sigma became much more widely known after other major corporations adopted it.

Organizations associated with early large-scale adoption included:

Motorola
AlliedSignal
General Electric

One of the most famous corporate advocates was Jack Welch, former CEO of General Electric (GE).

GE made Six Sigma a central management initiative during the 1990s.

This helped transform Six Sigma from something viewed primarily as a manufacturing quality methodology into a broader approach for:

Business improvement
Cost reduction
Operational excellence
Customer satisfaction
Management
Financial performance

ASQ notes that companies such as AlliedSignal and General Electric expanded Six Sigma with an emphasis not only on quality but also financial performance.

Core Objective of Six Sigma

The main objective is not merely:

"Find defective products."

It is:

"Find why the process creates defects and eliminate or control those causes."

Consider a company where 5% of invoices contain errors.

Traditional quality control might involve:

Checking invoices.
Finding incorrect invoices.
Correcting them.
Sending corrected invoices.

Six Sigma asks deeper questions:

Why are invoices incorrect?

Possible causes might include:

Incorrect customer master data
Manual data-entry errors
Poor software validation
Incorrect tax configuration
Inadequate employee training
Duplicate records
Poorly designed workflow

Instead of repeatedly correcting invoices, Six Sigma attempts to improve the underlying process.

The DMAIC Methodology

The most important framework associated with Six Sigma is:

DMAIC

DMAIC stands for:

D — Define

M — Measure

A — Analyze

I — Improve

C — Control

ASQ describes DMAIC as a structured problem-solving approach primarily used to improve existing processes that fail to meet performance standards or customer expectations.

Let's understand every stage.

1. DEFINE

The first step is clearly defining the problem.

The team determines:

What is wrong?
What process is affected?
Who is the customer?
What does the customer expect?
What is the project scope?
What improvement is required?
What business benefit is expected?

For example:

Problem: Customers wait an average of 45 minutes for technical support.

Goal: Reduce average waiting time to below 10 minutes.

Common Define-stage tools include:

Project Charter
SIPOC
Voice of Customer (VOC)
Critical to Quality (CTQ)
Process mapping
Stakeholder analysis

2. MEASURE

Now the organization collects reliable data.

Without accurate measurement, improvement becomes guesswork.

For example, an IT helpdesk might measure:

Number of tickets
Response time
Resolution time
Reopened tickets
Escalation rate
Customer satisfaction
First-call resolution
Technician workload

The objective is to establish the current baseline performance.

The principle is:

You cannot reliably improve something unless you understand its current performance.

3. ANALYZE

During Analyze, the team attempts to discover the root cause of the problem.

For example:

Why are support tickets taking too long?

Possible reasons:

Insufficient technicians
Poor ticket categorization
Slow escalation
Repetitive manual procedures
Inadequate knowledgebase
Software problems
Network delays
Incorrect priority allocation

Common analysis tools include:

Pareto charts
Fishbone/Ishikawa diagrams
5 Whys
Histograms
Scatter plots
Regression
Hypothesis testing
Cause-and-effect analysis
FMEA

The goal is to separate assumptions from causes supported by evidence.

4. IMPROVE

Once root causes have been identified, solutions are designed, tested and implemented.

For example:

An IT department may introduce:

Automatic ticket classification
Standard troubleshooting scripts
Better knowledgebase articles
Remote-support automation
Technician specialization
Improved escalation procedures

The team then measures whether these changes actually improve performance.

Possible Improve-stage tools include:

Design of Experiments (DOE)
Pilot testing
Kaizen
Brainstorming
Process redesign
Mistake proofing
Optimization

5. CONTROL

Improvement is not useful if the process returns to its previous condition after several months.

Therefore, Six Sigma includes a Control stage.

Organizations may introduce:

Dashboards
KPIs
Standard Operating Procedures
Control charts
Automated alerts
Periodic audits
Process ownership
Documentation
Training
Statistical Process Control

ASQ describes Control as the stage where mistake-proofing, long-term measurement, reaction plans and standard operating procedures are established to sustain improvement.

Simple DMAIC Example

Suppose an online company receives:

10,000 orders per month

and approximately:

500 orders are shipped late.

That represents a significant delivery problem.

Define

Problem:

5% of orders are shipped late.

Goal:

Reduce late shipments below 1%.

Measure

Collect information about:

Order time
Processing time
Warehouse time
Packing time
Courier pickup
Product availability

Analyze

The analysis discovers:

70% of late shipments occur because orders received after 3 PM are not assigned to warehouse staff until the next day.

Improve

The company introduces:

Automatic order assignment
Later warehouse processing
Additional evening packing
Automated courier scheduling

Control

A dashboard continuously monitors:

Late shipment percentage
Average processing time
Orders pending over 4 hours

If the late-shipment rate increases beyond an established limit, management receives an alert.

That is Six Sigma thinking in practice.

Important Six Sigma Concepts

Voice of Customer — VOC

VOC identifies what customers actually expect.

Examples:

Customers may want:

Faster delivery
Fewer errors
Reliable products
Quick technical support
Accurate invoices

Critical to Quality — CTQ

CTQ converts customer expectations into measurable requirements.

For example:

Customer expectation:

"I want fast support."

CTQ requirement:

90% of calls answered within 30 seconds.

Now "fast" becomes measurable.

SIPOC

SIPOC means:

Supplier → Input → Process → Output → Customer

It provides a high-level view of a process.

Example:

Supplier: Distributor

Input: Hardware

Process: Receive → Inspect → Configure → Deliver

Output: Configured computer

Customer: Business client

Pareto Analysis

Pareto analysis helps determine which problems contribute most significantly to the overall issue.

It is commonly associated with the 80/20 principle.

For example:

If 80% of support complaints arise from only 20% of recurring problems, solving those few problems can generate substantial improvement.

Fishbone Diagram

Also known as:

Cause-and-Effect Diagram

Ishikawa Diagram

It organizes possible causes of a problem.

Typical categories may include:

People
Process
Machines
Materials
Measurement
Environment

Five Whys

The 5 Whys technique repeatedly asks "Why?" to move from a visible symptom toward its underlying cause.

Example:

Server stopped.

Why?

Disk became full.

Why?

Log files consumed the disk.

Why?

Logs were never deleted.

Why?

No log-retention policy existed.

Root issue:

Missing log-management policy, rather than simply "disk full."

FMEA

FMEA stands for:

Failure Mode and Effects Analysis

It identifies ways in which a process, product or system might fail and helps prioritize risks before they create serious problems.

Statistical Process Control — SPC

SPC uses statistical methods and control charts to monitor process behavior.

The purpose is to distinguish between normal process variation and unusual conditions that require investigation.

Six Sigma Belt Levels

Six Sigma training commonly uses belt terminology inspired by martial arts.

The exact responsibilities and certification requirements can vary between organizations and certification bodies.

Common levels include:

White Belt

Introductory understanding.

Suitable for people who need basic awareness of Six Sigma terminology and concepts.

Yellow Belt

Understands basic tools and can participate in improvement projects.

Green Belt

More advanced practitioner who may manage smaller projects or participate significantly in larger Six Sigma projects.

Black Belt

Advanced Six Sigma practitioner capable of leading complex improvement projects and applying statistical analysis.

Master Black Belt

Highly experienced specialist who may:

Train Black Belts
Mentor project teams
Develop Six Sigma strategy
Guide enterprise implementation
Advise senior management

Champion/Sponsor

Usually a senior manager who supports projects, removes organizational barriers and ensures Six Sigma projects align with business objectives.

Six Sigma vs Lean

Six Sigma and Lean are related but originally developed with different emphases.

Six Sigma

Primarily focuses on:

Reducing variation and defects.

Lean

Primarily focuses on:

Eliminating waste and improving process flow.

Typical Lean wastes include unnecessary:

Waiting
Transportation
Inventory
Motion
Processing
Overproduction
Defects

ASQ explains that Lean focuses on waste and flow while Six Sigma focuses heavily on variation; organizations commonly combine them.

What Is Lean Six Sigma?

Lean Six Sigma combines Lean and Six Sigma.

In simple terms:

Lean = make the process faster and remove waste.

Six Sigma = make the process consistent and reduce defects.

Lean Six Sigma = make the process faster, more efficient and more reliable.

This combination is now widely used for operational and process improvement.

DMAIC vs DMADV

DMAIC is generally used for improving an existing process.

Another Six Sigma framework is:

DMADV

DMADV means:

Define → Measure → Analyze → Design → Verify

It is commonly associated with Design for Six Sigma (DFSS).

DMAIC

Use when:

An existing process needs improvement.

DMADV

Use when:

A new process/product needs to be designed or an existing one requires fundamental redesign.

Major Benefits of Six Sigma

1. Reduces Defects

The most obvious benefit is reducing errors, failures and defective output.

2. Reduces Costs

Defects create costs through:

Rework
Returns
Warranty
Wasted material
Support calls
Refunds
Replacement
Employee time

Reducing defects can therefore reduce operating expenses.

3. Improves Customer Satisfaction

Customers generally value:

Reliable products
Accurate billing
Fast service
Consistent quality
Timely delivery

Six Sigma directly targets the processes influencing these outcomes.

4. Improves Productivity

Employees spend less time correcting preventable mistakes.

5. Creates Data-Driven Decisions

Management decisions are based more heavily on:

Measurements
Statistics
Process data
Customer requirements
Verified root causes

rather than assumptions.

6. Reduces Process Variation

A good process should produce predictable results.

Six Sigma helps make processes more stable and consistent.

7. Improves Profitability

Lower defects, reduced waste, improved productivity and better customer retention can improve profitability.

ASQ associates Six Sigma improvements with reductions in errors and variation and potential improvements in profits, employee morale, customer satisfaction, and product/service quality.

8. Improves Employee Accountability

Processes become measurable.

Organizations can define:

KPIs
Owners
Targets
Responsibilities
Control procedures

9. Encourages Continuous Improvement

Six Sigma creates a structured culture where organizations continually identify and improve inefficient processes.

10. Improves Risk Management

Tools such as FMEA can help identify potential failures before they become serious problems.

Six Sigma in IT

Six Sigma can be particularly useful in IT operations.

Consider a technical-support company receiving 2,000 tickets monthly.

Possible measurements include:

First-response time
Resolution time
Reopen rate
Escalation percentage
First-call resolution
Customer satisfaction

Suppose analysis discovers:

40% of tickets concern password resets, printer problems and email configuration.

The company could develop:

Automated password reset
Standard printer diagnostic tools
Knowledgebase articles
Email configuration scripts
Remote diagnostic utilities

Ticket volume and resolution time can then be measured again.

That is a practical IT implementation of Six Sigma.

Six Sigma in Software Development

Six Sigma can help software teams monitor:

Defects per release
Failed deployments
Software crashes
API errors
Database failures
Support tickets
Testing defects
Code rework
Response time

For example:

A software product receives 500 support requests every month.

Analysis reveals:

60% concern only three recurring software defects.

Instead of continuously handling the tickets, developers identify and permanently correct the underlying causes.

This reduces:

Defects → Tickets → Support Cost → Customer Frustration

Six Sigma in Healthcare

Possible improvement targets include:

Patient waiting time
Laboratory report errors
Medication errors
Appointment delays
Billing errors
Equipment downtime
Sample rejection
Turnaround time

Six Sigma in Banking and Finance

Possible applications include:

Loan-processing time
Transaction errors
KYC errors
Customer complaints
Account-opening delays
Payment failures
Fraud-review processes
Document-processing errors

Six Sigma in Manufacturing

Manufacturing remains a major Six Sigma application area.

Organizations may measure:

Defective units
Scrap
Machine downtime
Production cycle time
Material waste
Rework
Warranty claims
Production variation

Six Sigma in Customer Service

Possible metrics include:

Call waiting time
First-call resolution
Average handling time
Complaint rate
Escalation rate
Customer satisfaction
Repeat calls

Six Sigma Is More Than Statistics

A common misconception is:

Six Sigma = complicated mathematics.

Statistics are important, particularly in advanced Six Sigma projects, but the broader methodology also involves:

Understanding customers
Mapping processes
Defining problems
Measuring performance
Finding root causes
Managing projects
Testing improvements
Standardizing procedures
Monitoring results

Therefore, Six Sigma is both a management methodology and analytical problem-solving framework.

Is Six Sigma Only for Large Companies?

No.

Small and medium-sized businesses can apply Six Sigma principles without establishing a huge Six Sigma department.

For example, a small computer-support company might discover:

100 monthly support calls.

35 are related to printer configuration.

Instead of repeatedly troubleshooting each computer, the company can:

Analyze common causes.
Standardize printer installation.
Create troubleshooting scripts.
Train engineers.
Publish knowledgebase articles.
Automate configuration where possible.
Measure support calls again.

If calls fall from 35 to 8 per month, the process improvement is measurable.

When Should Six Sigma Be Used?

Six Sigma is particularly useful when:

A problem repeatedly occurs.
Defect rates are high.
Customers regularly complain.
Costs are increasing.
Process performance is inconsistent.
Rework is excessive.
The root cause is unclear.
Reliable data is available or can be collected.
The problem has significant business impact.

When Six Sigma May Not Be Appropriate

Not every problem requires a full Six Sigma project.

For example:

A printer does not work because its power cable is disconnected.

The obvious solution is:

Reconnect the cable.

There is no need to launch a six-month DMAIC project.

Six Sigma becomes more valuable when a problem is:

Repetitive
Complex
Costly
High risk
Cross-functional
Difficult to diagnose
Supported by measurable data

Limitations of Six Sigma

Six Sigma also has limitations.

Training Requirements

Advanced statistical tools require knowledgeable personnel.

Implementation Cost

Training, software, consultants and dedicated employees may involve substantial costs.

Data Dependence

Incorrect or incomplete data can produce incorrect conclusions.

Excessive Bureaucracy

Poorly implemented Six Sigma programs can create unnecessary documentation and meetings.

Innovation Concerns

If organizations focus excessively on optimizing existing processes, they may underemphasize experimentation and radical innovation.

Therefore, Six Sigma should be applied intelligently rather than mechanically.

Six Sigma Certification

Six Sigma certification is available from various training and certification organizations.

Common certifications include:

Yellow Belt
Green Belt
Black Belt
Master Black Belt

Certification requirements are not universally identical.

Different organizations may have different requirements for:

Training
Examination
Work experience
Project completion
Recertification

ASQ, for example, offers formal Yellow Belt, Green Belt and Black Belt credentials.

Therefore, candidates should compare the reputation, examination structure and industry recognition of certification providers rather than assuming every "Six Sigma certificate" is equivalent.

Six Sigma and ISO 9001

Six Sigma and ISO 9001 are not the same.

ISO 9001

Provides requirements for establishing and maintaining a Quality Management System.

Six Sigma

Provides methodologies and tools for improving process performance and reducing variation.

Organizations can therefore use both.

ISO 9001 provides a quality-management framework.

Six Sigma can provide structured techniques for improving processes within that framework.

Six Sigma and Quality Control

Quality Control often asks:

"Is this output defective?"

Six Sigma asks:

"Why is the process creating defective output?"

The difference is important.

Detecting defects is useful.

Preventing their recurrence is usually more valuable.

The Six Sigma Mindset

Six Sigma encourages organizations to move from:

Opinion → Data

Symptom → Root Cause

Inspection → Prevention

Temporary Fix → Permanent Improvement

Individual Guesswork → Structured Process

Uncontrolled Change → Measured Improvement

This mindset is arguably more important than memorizing every Six Sigma statistical formula.

Frequently Asked Questions (FAQ)

1. What is Six Sigma in simple words?

Six Sigma is a structured method of improving a process by using data to identify the causes of errors and variation and then eliminating or controlling those causes.

2. Who invented Six Sigma?

Six Sigma originated at Motorola during the 1980s. Engineer Bill Smith is widely regarded as its principal originator, while Motorola CEO Bob Galvin was instrumental in promoting and deploying it across the company.

3. When was Six Sigma developed?

Six Sigma was developed during the 1980s at Motorola, with Motorola's initial Six Sigma system being deployed in 1987.

4. What does Sigma mean?

Sigma (σ) is the Greek letter commonly used in statistics to represent standard deviation, a measure of variation.

5. What is the Six Sigma defect target?

The commonly cited Six Sigma benchmark is approximately 3.4 defects per million opportunities (DPMO).

6. What is DMAIC?

DMAIC means:

Define, Measure, Analyze, Improve and Control.

It is the primary structured problem-solving roadmap used to improve existing processes in Six Sigma.

7. What is DMADV?

DMADV means:

Define, Measure, Analyze, Design and Verify.

It is generally used when designing a new product or process or undertaking a fundamental redesign.

8. What is Lean Six Sigma?

Lean Six Sigma combines Lean's focus on eliminating waste and improving flow with Six Sigma's focus on reducing defects and process variation.

9. What are Six Sigma Belts?

Common Six Sigma competency levels include:

White Belt, Yellow Belt, Green Belt, Black Belt and Master Black Belt.

10. Which Six Sigma Belt is best for beginners?

White Belt or Yellow Belt is generally suitable for basic introductory knowledge. Green Belt is more appropriate for professionals who want to participate actively in process-improvement projects.

11. Is Six Sigma useful in IT?

Yes. It can be applied to incident management, technical support, server availability, software defects, cybersecurity processes, service-desk performance, deployment failures and other measurable IT processes.

12. Is Six Sigma only for manufacturing?

No. It is now applied across manufacturing, healthcare, finance, services, IT, logistics, education and many other industries.

13. Does Six Sigma require mathematics?

Basic Six Sigma concepts require relatively little advanced mathematics. Green Belt and especially Black Belt work can involve more substantial statistics.

14. What is DPMO?

DPMO means:

Defects Per Million Opportunities.

It provides a standardized way of describing process defect performance.

15. What is a defect in Six Sigma?

A defect is an output or condition that fails to meet a defined customer requirement, specification or quality criterion.

16. What is process variation?

Process variation refers to differences in process outputs over time. Excessive or uncontrolled variation can create inconsistent quality and defects.

17. What is Voice of Customer?

Voice of Customer (VOC) refers to identifying and understanding customer needs, expectations and requirements.

18. What is CTQ?

CTQ means Critical to Quality. It translates customer requirements into measurable characteristics that a process or product must satisfy.

19. What is SIPOC?

SIPOC means:

Supplier, Input, Process, Output, Customer.

It is a high-level process-mapping technique commonly used during the Define phase.

20. What is the main benefit of Six Sigma?

Its central benefit is improving process performance through measurable reductions in defects and variation. This can also improve costs, productivity, quality and customer satisfaction.

21. What is the difference between Six Sigma and Lean?

Lean primarily targets waste and flow, while Six Sigma primarily targets defects and variation.

22. What is the difference between Six Sigma and ISO 9001?

ISO 9001 specifies requirements for a quality-management system, whereas Six Sigma provides methodologies and analytical tools for improving processes.

23. Can small businesses implement Six Sigma?

Yes. A small organization can apply DMAIC and basic Six Sigma tools without creating a large formal Six Sigma department.

24. Is Six Sigma certification compulsory?

No. Organizations can use Six Sigma methods without certification. Certification demonstrates knowledge or competency according to the certifying organization's requirements.

25. Is Six Sigma still relevant?

Yes. The terminology may coexist with Lean, Agile, DevOps, continuous improvement and modern data analytics, but its core concepts—measurement, variation reduction, root-cause analysis, experimentation and process control—remain highly applicable.

Conclusion

Six Sigma started as a quality-improvement initiative at Motorola in the 1980s, with engineer Bill Smith playing the central role in its development and CEO Bob Galvin providing critical organizational leadership. It later became globally recognized through adoption by companies including AlliedSignal and General Electric.

Its greatest contribution is not simply the famous 3.4 defects per million opportunities benchmark. Its real value is a disciplined way of thinking:

Define the problem.

Measure what is actually happening.

Analyze the root cause.

Improve the process based on evidence.

Control the improved process so the problem does not return.

That philosophy is represented by DMAIC — Define, Measure, Analyze, Improve and Control.

Six Sigma can therefore be useful anywhere an organization has repeatable and measurable processes—whether it manufactures millions of components, processes financial transactions, runs a hospital, develops software, operates servers or handles customer-support tickets.

When implemented correctly, Six Sigma changes an organization's approach from repeatedly fixing problems to systematically improving the processes that create those problems.