UNIT V QUALITY STANDARDTopics Covered:

Need for standards ISO 9000 series ISO 9000-3 series CMM and CMMI Six Sigma Concepts

Need for Standards:Standardization (or standardisation) is the process of agreeing on technical standards. A standard is

a document that establishes uniform engineering or technical specifications, criteria, methods, processes, or practices. Some standards are mandatory while others are voluntary. Some standards are defacto, meaning informal practices followed out of convenience, or dejure, meaning formal requirements. Formal standards bodies such as the International Standard Organisation(ISO) or the American National Standard University are independent of the manufacturers of the goods for which they publish standards.The goals of standardization can be to help with independence of single suppliers (commodification), compatibility, interoperability, safety, repeatability, or quality.In social sciences, including economics, the idea of standardization is close to the solution for a coordination problem, a situation in which all parties can realize mutual gains, but only by making mutually consistent decisions. Standardization is the process for select better choices and ratificate this consistent decisions, as an obtained standard.Types of standardization process:

Emergence in de facto use: tradition (old standards on countries) and/or domination (Microsoft ex.).

Fixed by a standard body: o in an impositive process: usually in mandatory norms (like dictatorial

Laws). o in a consensus process: usually for voluntary standards

standardization is defined as: The development and implementation of concepts, doctrines, procedures and designs to achieve and maintain the required levels of compatibility, interchangeability or commonality in the operational, procedural, material, technical and administrative fields to attain interoperability

ISO 9000 Series:ISO 9000 is a family of standards for quality management systems. ISO 9000 is

maintained by ISO, the International Organization for Standardization and is administered by accreditation and certification bodies. ISO-9001 covers the entire process from product design through after sales service. ISO-9002 covers only the manufacture (or a specific service such as a QC/QA laboratory) of the product. ISO-9003 covers the "final inspection" of the product only. ISO-9004 is an "Internal Use" standard - it cannot be registered and is not subject to the third party audits.

Fundamental principles of ISO 9001 standards

ISO-9001:

Some of the requirements in ISO 9001 (which is one of the standards in the ISO 9000 family) would include

a set of procedures that cover all key processes in the business; monitoring processes to ensure they are effective; keeping adequate records; checking output for defects, with appropriate corrective action where

necessary; regularly reviewing individual processes and the quality system itself for

effectiveness; and facilitating continual improvement

ISO 9001:2000 specifies requirements for a quality management system where an organization

1. needs to demonstrate its ability to consistently provide product that meets customer and applicable regulatory requirements, and

2. aims to enhance customer satisfaction through the effective application of the system, including processes for continual improvement of the system and the assurance of conformity to customer and applicable regulatory requirements.

All requirements of this International Standard are generic and are intended to be applicable to all organizations, regardless of type, size and product provided.

Clauses of the standard

Where any requirement(s) of this International Standard cannot be applied due to the nature of an organization and its product, this can be considered for exclusion.

ISO-9002:• ISO 9002, first published in 1987, described how to implement a Quality

Management System for the manufacture and delivery of products.

• There were 18 sections for which a documented procedure needed to be written, and the mantra of the standard was “Document what you do, then do what you document.”

• The standard was focused on industries that produced products rather than service-based industries.

• Note: ISO 9001 was identical to ISO 9002 with the addition of requirements for design control and product service

ISO-9003:ISO 9003 ISO 9003, provided requirements for a Quality Management System exclusively for inspections and testing, and basically stripped away any requirements that dealt with the manufacture or servicing of products. This standard was used almost exclusively by warehouse and resale industries where the company itself did not manufacture the parts, but only stocked and sold the product. These industries would be focused on ensuring that product they purchased was properly inspected in order to meet the needs of customers they re-sold the product• In 2000, ISO 9001 was updated from a “document everything” approach to a more

process-based approach for Quality Management Systems. • This also made the standard more applicable to service-based industries and added

the ability of a company to exclude certain sections of the requirements, such as design for companies that only build to customer design.

• By allowing the exclusions from some requirements, the need for separate documents (ISO 9001, ISO 9002 & ISO 9003) was removed and the ISO 9002 & ISO 9003 standards were rendered obsolete.

From 2000 onward, companies could not have their Quality Management System certified to ISO 9002 or ISO 9003, and a company could only certify an ISO 9001 Quality Management System

ISO 9000-3 renamed as ISO90003 is a quality management standard for software products and related services and divided into the following sections

• Quality System Requirements and Four Key areas1. Management Responsibility2. Resource Management3. Product Realization4. Measurement, Analysis & Improvement

4.   SYSTEMIC REQUIREMENTS AND GUIDELINES 4.1 Organizational requirements and guidelines4.2 Documentation requirements and guidelines4.2.2 Develop a quality manual4.2.3 Control quality documents4.2.4 Maintain quality records4.2.4.1 Show that requirements are being met4.2.4.2 Demonstrate that your QMS is effective4.2.4.3 Control record retention and disposition5.   MANAGEMENT REQUIREMENTS AND GUIDELINES 5.1 Commitment requirements and guidelines5.2 Customer requirements and guidelines5.3 Policy requirements and guidelines5.4 Planning requirements and guidelines5.4.1 Establish quality objectives5.4.2 Carry out quality planning5.5 Managerial requirements and guidelines5.5.2 Appoint management representative5.5.3 Establish internal communications5.6 Review requirements and guidelines5.6.1 Perform reviews at planned intervals5.6.2 Examine management review inputs5.6.3 Generate management review outputs 6.   RESOURCE REQUIREMENTS AND GUIDELINES 6.1 Allocation requirements and guidelines 6.2 Personnel requirements and guidelines 6.2.1 Provide competent personnel 6.2.2 Meet competence requirements 6.3 Infrastructure requirements and guidelines 6.4 Environmental requirements and guidelines 7.PRODUCT   REALIZATION REQUIREMENTS AND GUIDELINES 7.1.1 Use life cycle models to plan work 7.1.2 Carry out software quality planning 7.2 Customer requirements and guidelines 7.2.1.1 Determine customer-related requirements 7.2.1.2 Determine additional product requirements 7.2.2 Consider your product-oriented requirements 7.2.2.1 Review contractual issues and concerns 7.2.2.2 Evaluate risk before agreeing to supply software 7.2.2.3 Appoint someone to represent the customer 7.2.3 Establish effective customer communications 7.2.3.1 Consider the type and extent of your contractual obligations 7.2.3.2 Schedule joint reviews during software development projects 7.2.3.3 Communicate with customers during operations and maintenance 7.3 Development requirements and guidelines 7.3.1.1 Plan the design and development of software products

7.3.1.2 Plan your review, verification, and validation activities 7.3.1.3 Plan your design and development work assignments 7.3.1.4 Plan design and development boundaries and interfaces 7.3.2 Define product design and development inputs 7.3.3 Generate product design and development outputs 7.3.4 Perform product design and development reviews 7.3.5 Conduct product design and development verifications 7.3.6 Carry out product design and development validations 7.3.6.2 Carry out planned software testing activities 7.3.7 Control product design and development changes 7.4 Purchasing requirements and guidelines 7.4.1.1 Control purchased products and services 7.4.1.2 Control the use of external resources 7.4.2 Clarify purchasing information 7.4.3 Verify purchased products 7.5 Production requirements and guidelines7.5.1 Control production and service provision 7.5.1.1 Control software production and service activities 7.5.1.2 Control software build and release activities 7.5.1.3 Control software replication activities 7.5.1.4 Control software product delivery activities 7.5.1.5 Control software product installation activities 7.5.1.6 Control software operation and support activities 7.5.1.7 Control software product maintenance activities 7.5.2 Validate processes if outputs cannot be verified 7.5.3 Identify your products and establish traceability 7.5.3.1 Use configuration management to identify and track software 7.5.3.2 Clarify scope of software configuration management process 7.5.3.3 Establish a process to trace your software components 7.5.4 Protect customer property supplied for products 7.5.5 Preserve software products and components 8. MEASUREMENT, ANALYSIS & IMPROVEMENT GUIDELINES 8. Remedial requirements and guidelines 8.1 Planning requirements and guidelines 8.2 Research requirements and guidelines 8.2.3 Find out if processes achieve planned results 8.2.4 Verify that quality requirements are being met 8.3 Control requirements and guidelines 8.4 Analytical requirements and guidelines 8.5 Implementation requirements and guidelines 8.5.1 Improve quality management system 8.5.2 Correct actual nonconformities 8.5.3 Prevent potential nonconformities

Capability maturity model (CMM)CMM was developed by the Software Engineering Institute (SEI) at Carnegie Mellon University in 1987.

It is not a software process model. It is a framework which is used to analyze the approach and techniques followed by any organization to develop a software product.

It also provides guidelines to further enhance the maturity of those software products. It is based on feedback and development practices adopted by the most successful

organizations worldwide. This model describes a strategy that should be followed by moving through 5 different

levels. Each level of maturity shows a process capability level. All the levels except level-1

are further described by Key Process Areas (KPA’s).Key Process Areas (KPA’s):Each of these KPA’s defines the basic requirements that should be met by a software process in order to satisfy the KPA and achieve that level of maturity.Conceptually, key process areas form the basis for management control of the software project and establish a context in which technical methods are applied, work products like models, documents, data, reports, etc. are produced, milestones are established, quality is ensured and change is properly managed.

The 5 levels of CMM are as follows:

Level-1: Initial – No KPA’s defined. Processes followed are adhoc and immature and are not well defined. Unstable environment for software dvelopment. No basis for predicting product quality, time for completion, etc.

Level-2: Repeatable –Focuses on establishing basic project management policies.Experience with earlier projects is used for managing new similar natured projects.

KPA’s: 1. Project Planning- It includes defining resources required, goals, constraints, etc.

for the project. It presents a detailed plan to be followed systematically for successful completion of a good quality software.

2. Configuration Management- The focus is on maintaining the performance of the software product, including all its components, for the entire lifecycle.

3. Requirements Management- It includes the management of customer reviews and feedback which result in some changes in the requirement set. It also consists of accommodation of those modified requirements.

4. Subcontract Management- It focuses on the effective management of qualified software contractors i.e. it manages the parts of the software which are developed by third parties.

5. Project tracking and oversight- it establishes adequate visibility into actual progress and take effective actions for deviations.

6. Software Quality Assurance- It guarantees a good quality software product by following certain rules and quality standard guidelines while development.

Level-3: Defined – At this level, documentation of the standard guidelines and procedures takes place. It is a well defined integrated set of project specific software engineering and

management processes.KPA’s:

1. Peer Reviews- In this method, defects are removed by using a number of review methods like walkthroughs, inspections, buddy checks, etc.

2. Intergroup Coordination- It consists of planned interactions between different development teams to ensure efficient and proper fulfilment of customer needs.

3. Organization Process Definition- It’s key focus is on the development and maintenance of the standard development processes.

4. Organization Process Focus- It includes activities and practices that should be followed to improve the process capabilities of an organization.

5. Training Programs- It focuses on the enhancement of knowledge and skills of the team members including the developers and ensuring an increase in work efficiency.

6. Software Product Engineering- Technical activities of the product are well-defined(SDLC)

7. Integrated software management- It integrates

Level-4: Managed – At this stage, quantitative quality goals are set for the organization for software

products as well as software processes. The measurements made help the organization to predict the product and process

quality within some limits defined quantitatively.KPA’s:

1. Software Quality Management- It includes the establishment of plans and strategies to develop a quantitative analysis and understanding of the product’s quality.

2. Quantitative Management- It focuses on controlling the project performance in a quantitative manner.

Level-5: Optimizing – This is the highest level of process maturity in CMM and focuses on continuous

process improvement in the organization using quantitative feedback. Use of new tools, techniques and evaluation of software processes is done to prevent

recurrence of known defects.KPA’s:

1. Process Change Management- Its focus is on the continuous improvement of organization’s software processes to improve productivity, quality and cycle time for the software product.

2. Technology Change Management- It consists of identification and use of new technologies to improve product quality and decrease the product development time.

3. Defect Prevention- It focuses on identification of causes of defects and to prevent them from recurring in future projects by improving project defined process.

Advantages of CMM It allows for improvement an devolution Also used in conjunction with other quality standards It highlights the defects as they occur. The CMM prioritizes tasks for improvement It provides a matrix for strengths and weakness

5 Stages And 6 Measurements of CMM

The maturity model seeks to measure how well these processes are carried out. There are five stages to six measurement categories in

subjectively rating an organization’s quality operation.

The five stages are:1. Uncertainty, where management is confused and

uncommitted regarding quality management tool2. Awakening, where management is beginning to recognize

that quality management can help3. Enlightenment, where the decision is made to conduct a

formal quality improvement programme4. Wisdom ,where the company has the chance to make changes

permanent(things are basically quiet and people wonder why they used to have problems);

5. Certainty, where quality management is considered an absolutely vital part of company management.

The six measurement categories are:1. Management understanding and attitude, characterized as ‘no

comprehension of quality as a management tool’ at uncertainty and ‘an essential part of the company system’ at certainty;

2. Quality organization status, characterized as hidden at uncertainty and a thought leader/ main concern at certainty;

3. Problem handling, which are fought when they occur at uncertainty and prevented at certainty;

4. Cost of quality as percentage of sales, characterized as 20% at uncertainty and 2.5% at certainty;

5. Quality improvement actions, characterized as no organized activities at uncertainty and a normal and continued activity at certainty;

6. Summation of company quality posture, summarized as ‘we do not know why we have problems with quality’ at uncertainty and ‘we know why we do not have problems with quality’ at certainty.

Evolution of the CMMYear Version published1987 Software process maturity framework1987 Preliminary maturity questionnaire1987 Characterizing the software process1989 Managing th software process1990 DraftversionofCMMv0.21991 CMMv0.6discussion1991 CMMv1.01993 CMMv1.1

Capability Maturity Model Integration-CMMI

CMM Integration project was formed to sort out the problem of using multiple CMMs. CMMI product team's mission was to combine three Source Models into a single improvement framework for the organizations pursuing enterprise-wide process improvement. These three Source Models are −

Capability Maturity Model for Software (SW-CMM) - v2.0 Draft C. Electronic Industries Alliance Interim Standard (EIA/IS) - 731 Systems

Engineering. Integrated Product Development Capability Maturity Model (IPD-CMM) v0.98.

CMM Integration Builds an initial set of integrated models. Improves best practices from source models based on lessons learned. Establishes a framework to enable integration of future models. CMMI is the successor of the CMM and evolved as a more matured set of

guidelines and was built combining the best components of individual disciplines of CMM(Software CMM, People CMM, etc.). It can be applied to product manufacturing, people management, software development, etc.

CMM describes about the software engineering alone where as CMM Integrated describes both software and system engineering. CMMI also incorporates the Integrated Process and Product Development and the supplier sourcing.

The objectives of CMMI are as follows − Produce quality products or services − The process-improvement concept in

CMMI models evolved out of the Deming, Juran, and Crosby quality paradigm: Quality products are a result of quality processes. CMMI has a strong focus on quality-related activities including requirements management, quality assurance, verification, and validation.

Create value for the stockholders − Mature organizations are more likely to make better cost and revenue estimates than those with less maturity, and then perform in line with those estimates. CMMI supports quality products, predictable schedules, and effective measurement to support the management in making accurate and defensible forecasts. This process maturity can guard against project performance problems that could weaken the value of the organization in the eyes of investors.

Enhance customer satisfaction − Meeting cost and schedule targets with high quality products that are validated against customer needs is a good formula for customer satisfaction. CMMI addresses all of these ingredients through its emphasis on planning, monitoring, and measuring, and the improved predictability that comes with more capable processes.

Increase market share − Market share is a result of many factors, including quality products and services, name identification, pricing, and image. Customers like to deal with suppliers who have a reputation for meeting their commitments.

Gain an industry-wide recognition for excellenceThe best way to develop a reputation for excellence is to consistently perform well on projects, delivering

quality products and services within cost and schedule parameters. Having processes that conform to CMMI requirements can enhance that reputation.

The CMM Integration is a model that has integrated several disciplines/bodies of knowledge. Currently there are four bodies of knowledge available to you when selecting a CMMI model.

Systems EngineeringSystems engineering covers the development of complete systems, which may or may not include software. Systems engineers focus on transforming customer needs, expectations, and constraints into product solutions and supporting these product solutions throughout the entire lifecycle of the product.

Software EngineeringSoftware engineering covers the development of software systems. Software engineers focus on the application of systematic, disciplined, and quantifiable approaches to the development, operation, and maintenance of software.

Integrated Product and Process DevelopmentIntegrated Product and Process Development (IPPD) is a systematic approach that achieves a timely collaboration of relevant stakeholders throughout the life of the product to better satisfy customer needs, expectations, and requirements. The processes to support an IPPD approach are integrated with the other processes in the organization.

Supplier SourcingAs work efforts become more complex, project managers may use suppliers to perform functions or add modifications to products that are specifically needed by the project. When those activities are critical, the project benefits from enhanced source analysis and from monitoring supplier activities before product delivery. Under these circumstances, the supplier sourcing discipline covers the acquisition of products from suppliers

The CMMI is structured as follows − Maturity Levels (staged representation) or Capability Levels (continuous

representation) Process Areas Goals: Generic and Specific Common Features Practices: Generic and Specific

Process Area:A process area is a cluster of related practices in an area that, whenimplemented collectively, satisfies a set of goals consideredimportant for making significant improvement in that area.

Specific Goals:A specific goal describes the unique characteristics that must be

present to satisfy the process area.Specific Practices:

The activities expected to result in achievement of specific goals

Generic Goals and PracticesGoal 1: Achieve Specific Goals:Practices:Perform base practices to develop work products and provide services toAchieve the specific goals of the process area.Goal 2: Institutionalize a Managed Process:Practices:• Establish an organization policy• Plan the process• Provide Resources• Assign Responsibility• Train People• Manage Configurations• Identify and involve relevant stake holders• Monitor and control the process• Objectively evaluate adherence• Review status with high level management

Goal 3: Institutionalize a Defined Process:Practices:• Establish a defined process

• Collect improvement informationGoal 4: Institutionalize a Quantitatively managed Process:Practices:• Establish quantitative objectives for the process• Stabilize sub process performanceGoal 5: Institutionalize an Optimizing Process:Practices:• Ensure continuous process improvement• Correct Root Cause of Problems

A representation allows an organization to pursue different improvement objectives. An organization can go for one of the following two improvement paths.

A representation allows an organization to pursue different improvement objectives. An organization can go for one of the following two improvement paths.

Staged RepresentationThe staged representation is the approach used in the Software CMM. It is an approach that uses predefined sets of process areas to define an improvement path for an organization. This improvement path is described by a model component called a Maturity Level. A maturity level is a well-defined evolutionary plateau towards achieving improved organizational processes.

CMMI Staged Representation Provides a proven sequence of improvements, each serving as a foundation for the

next. Permits comparisons across and among organizations by the use of maturity levels. Provides an easy migration from the SW-CMM to CMMI. Provides a single rating that summarizes appraisal results and allows comparisons

among organizations.Thus Staged Representation provides a pre-defined roadmap for organizational improvement based on proven grouping and ordering of processes and associated organizational relationships. You cannot divert from the sequence of steps.

CMMI Staged StructureFollowing picture illustrates CMMI Staged Model Structure.

CMMI Continuous RepresentationContinuous representation is the approach used in the SECM and the IPD-CMM. This approach allows an organization to select a specific process area and make improvements based on it. The continuous representation uses Capability Levels to characterize improvement relative to an individual process area.

Allows you to select the order of improvement that best meets your organization's business objectives and mitigates your organization's areas of risk.

Enables comparisons across and among organizations on a process-area-by-process-area basis.

Provides an easy migration from EIA 731 (and other models with a continuous representation) to CMMI.

Thus Continuous Representation provides flexibility to organizations to choose the processes for improvement, as well as the amount of improvement required.CMMI Continuous StructureThe following picture illustrates the CMMI Continuous Model Structure.

Continuous vs Staged Representations

Continuous Representation

Staged Representation

Process areas are organized by process area categories.

Process areas are organized by maturity levels.

Improvement is measured using capability levels. Capability levels measure the maturity of a particular process across an organization; it ranges from 0 through 5.

Improvement is measured using maturity levels. Maturity levels measure the maturity of a set of processes across an organization: it ranges from 1 through 5.

There are two types of specific practices: base and advanced. All specific practices

There is only one type of specific practice. The concepts of base and advanced practices are not

appear in the continuous representation.

used. All specific practices appear in the staged representation except when a related base-advanced pair of practices appears in the continuous representation, in which case only the advanced practice appears in the staged representation.

Capability levels are used to organize the generic practices.

Common features are used to organize generic practices.

All generic practices are included in each process area.

Only the level 2 and level 3 generic practices are included.

Equivalent staging allows determination of a maturity level from an organization's achievement profile.

There is no need for an equivalence mechanism to back the continuous representation because each organization can choose what to improve and how much to improve using the staged representation.

CMMI models with staged representation, have five maturity levels designated by the numbers 1 through 5. They are −

Initial Managed Defined Quantitatively Managed Optimization

The following image shows the maturity levels in a CMMI staged representation.

.

A capability level is a well-defined evolutionary plateau describing the organization's capability relative to a process area. A capability level consists of related specific and generic practices for a process area that can improve the organization's processes associated with that process area. Each level is a layer in the foundation for continuous process improvement.Thus, capability levels are cumulative, i.e., a higher capability level includes the attributes of the lower levels.

In CMMI models with a continuous representation, there are six capability levels designated by the numbers 0 through 5.

0 − Incomplete1 − Performed2 − Managed3 − Defined4 − Quantitatively Managed5 − Optimizing

A short description of each capability level is as follows −Capability Level 0: IncompleteAn "incomplete process" is a process that is either not performed or partially performed. One or more of the specific goals of the process area are not satisfied and no generic goals exist for this level since there is no reason to institutionalize a partially performed process.

This is tantamount to Maturity Level 1 in the staged representation.Capability Level 1: PerformedA Capability Level 1 process is a process that is expected to perform all of the Capability Level 1 specific and generic practices. Performance may not be stable and may not meet specific objectives such as quality, cost, and schedule, but useful work can be done. This is only a start, or baby-step, in process improvement. It means that you are doing something but you cannot prove that it is really working for you.Capability Level 2: ManagedA managed process is planned, performed, monitored, and controlled for individual projects, groups, or stand-alone processes to achieve a given purpose. Managing the process achieves both the model objectives for the process as well as other objectives, such as cost, schedule, and quality. As the title of this level indicates, you are actively

managing the way things are done in your organization. You have some metrics that are consistently collected and applied to your management approach.Note − metrics are collected and used at all levels of the CMMI, in both the staged and continuous representationsCapability Level 3: DefinedA capability level 3 process is characterized as a "defined process." A defined process is a managed (capability level 2) process that is tailored from the organization's set of standard processes according to the organization's tailoring guidelines, and contributes work products, measures, and other process-improvement information to the organizational process assets.Capability Level 4: Quantitatively ManagedA capability level 4 process is characterized as a "quantitatively managed process." A quantitatively managed process is a defined (capability level 3) process that is controlled using statistical and other quantitative techniques. Quantitative objectives for quality and process performance are established and used as criteria in managing the process. Quality and process performance is understood in statistical terms and is managed throughout the life of the process.Capability Level 4 focuses on establishing baselines, models, and measurements for process performance.

Capability Level 5: Optimizing An optimizing process is a quantitatively managed process that is improved, based on an understanding of the common causes of process variation inherent to the process. It focuses on continually improving process performance through both incremental and innovative improvements. Both the defined processes and the organization's set of standard processes are the targets of improvement activities.Capability Level 5 focuses on studying performance results across the organization or entire enterprise, finding common causes of problems in how the work is done (the process[es] used), and fixing the problems in the process. The fix would include updating the process documentation and training involved where the errors were injected.

SIX SIGMA CONCEPT: Six Sigma at many organizations simply means a measure of quality that strives for near perfection. Six Sigma is a disciplined, data-driven approach and methodology for eliminating defects (driving towards six standard deviations between the mean and the nearest specification limit) in any process -- from manufacturing to transactional and from product to service.The term Six Sigma represents a stringent level of quality. It is a specific defect rate:3.4 defective parts per million(ppm).It was made known in the industry by Motorola, Inc.,Six Sigma has become an industry standard as an ultimate quality goal. Sigma(s)is the Greek symbol for standard deviation.

Six Sigma is a set of practices originally developed by Motorola to systematically improve processes by eliminating defects. A defect is defined as nonconformity of a product or service to its specifications.

While the particulars of the methodology were originally formulated by Bill Smith at Motorola in 1986, Six Sigma was heavily inspired by six preceding decades of quality improvement methodologies such as quality control, TQM, and Zero Defects. Like its predecessors, Six Sigma asserts the following:

Continuous efforts to reduce variation in process outputs is key to business success Manufacturing and business processes can be measured, analyzed, improved and

controlled Succeeding at achieving sustained quality improvement requires commitment from

the entire organization, particularly from top-level management

Sigma (the lower-case Greek letter σ) is used to represent standard deviation (a measure of variation) of a population (lower-case 's', is an estimate, based on a sample). The term "six sigma process" comes from the notion that if one has six standard deviations between the mean of a process and the nearest specification limit, there will be practically no items that fail to meet the specifications.

As the following figure1indicates, the areas under the curve of normal distribution defined by standard deviations are constants in terms of percentages, regardless of the distribution parameters.The area under the curve as defined by plus and minus one standard deviation(sigma)From the mean is 8.26%.The area defined by plus/minus two standard deviations is 95.44%,andsoforth.Thearea defined by plus/minus six sigma is 99.9999998%.The area out side the six sigma area is thus 100%-99.9999998%=0.0000002%.

Fig.1

The area within the six sigma limit as the percentage of defect-free parts and the area outside the limit as the percentage of defective parts, it is found that six sigma is equal to2 defectives per billion parts or 0.002 defective parts per million.

The interpretation of defect rate as it relates to the normal distribution will be clearer if we include the specification.Given the specification limits(which were derived from customers' requirements), our purpose is to produce parts or products within the limits. Parts or products outside the specification limits do not conform to requirements. If we can reduce the variations in the production process so that the six sigma (standard deviations)variation of the production

process is within the specification limits, then we will have six sigma quality level.

Fig.2SpecificationLimits,Centered sixsigma, andShifted sixsigma

The six sigma value of 0.002 ppm is from the statistical normal distribution. It assumes that each execution of the production process will produce the exact distribution of parts or products centered with regard to the specification limits. In reality, however, process shifts and drifts always result from variations in process execution.

The maximum process shifts as indicated by research is 1.5sigma. If we account for this 1.5-sigma shift in the production process, we will get the value of 3.4ppm.Such shifting is illustrated in the two lower panels of fig.2.Given fixed specification limits, the distribution of the production process may shift to the left or to the right. When the shift is 1.5sigma, the area outside the specification limit on one end is 3.4ppm, and on the other it is nearly zero.

The slight difference between the centered six sigma and the shifted six sigma may imply something significant. The former is practically equivalent to zero defects, which may invite the debate whether it is feasible to achieve such a goal.

In order to reach six sigma, we have to improve the process. Specifically, we must reduce process variations so that the six sigma variation is still within the specification limits.

The concept and approach of six sigma has been expanded and applied to the improvement of management systems and total quality management.

The statistical representation of Six Sigma describes quantitatively how a process is performing. To achieve Six Sigma, a process must not produce more than 3.4 defects per million opportunities. A Six Sigma defect is defined as anything outside of customer specifications. A Six Sigma opportunity is then the total quantity of chances for a defect. Process sigma can easily be calculated using a Six-Sigma calculator.

The fundamental objective of the Six Sigma methodology is the implementation of a measurement-based strategy that focuses on process improvement and variation reduction through the application of Six Sigma improvement projects. This is accomplished through the use of two Six Sigma sub-methodologies: DMAIC and DMADV. The Six Sigma DMAIC process (define, measure, analyze, improve, control) is an improvement system for existing processes falling below specification and looking for incremental improvement. The Six Sigma DMADV process (define, measure, analyze, design, verify) is an improvement system used to develop new processes or products at Six Sigma quality levels. It can also be employed if a current process requires more than just incremental improvement. Both Six Sigma processes are executed by Six Sigma Green Belts and Six Sigma Black Belts, and are overseen by Six Sigma Master Black Belts.