Six Sigma has become very popular throughout the whole world. There are several reasons for this popularity. First, it is regarded as a fresh quality management strategy which can replace TQC, TQM and others.
Many companies, which were not quite successful in implementing previous management strategies such as TQC and TQM, are eager to introduce Six Sigma.
Development process of Six Sigma in quality management
Six Sigma is viewed as a systematic, scientific, statistical and smarter (4S) approach for management innovation which is quite suitable for use in a knowledge-based information society.
Second, Six Sigma provides efficient manpower cultivation and utilization. It employs a “belt system” in which the levels of mastery are classified as green belt, black belt, master black belt and champion. As a person in a company obtains certain
training, he acquires a belt. Usually, a black belt is the leader of a project team and several green belts work together for the project team.
Third, there are many success stories of Six Sigma application in well known world-class companies. As mentioned earlier, Six Sigma was pioneered by Motorola and launched as a strategic initiative in 1987. Since then, and particularly from 1995, an exponentially growing number of prestigious global firms have launched a Six Sigma program. It has been noted that many globally leading companies run Six Sigma programs (see Figure 3), and it has been well known that Motorola, GE, Allied Signal, IBM, DEC, Texas Instruments, Sony, Kodak, Nokia, and Philips Electronics among others have been quite successful in Six Sigma. In Korea, the Samsung, LG, Hyundai groups and Korea Heavy Industries & Construction Company have been quite successful with Six Sigma.
Lastly, Six Sigma provides flexibility in the new millennium of 3Cs, which are:
• Change: Changing society
• Customer: Power is shifted to customer and customer demand is high
• Competition: Competition in quality and productivity
The pace of change during the last decade has been unprecedented, and the speed of change in this new millennium is perhaps faster than ever before. Most notably, the power has shifted from producer to customer. The producer-oriented industrial society is over, and the customer-oriented information society has arrived. The customer has all the rights to order, select and buy goods and services. Especially, in e-business, the customer has all-mighty power.
Six Sigma with its 4S(systematic, scientific, statistical and smarter) approaches provides flexibility in managing a business unit.
Monday, August 31, 2009
Quality Characteristic in ISO 9000
Any feature or characteristic of a product or service that is needed to satisfy
customer needs or achieve fitness for use is a quality characteristic. When
dealing with products the characteristics are almost always technical character-
istics, whereas service quality characteristics have a human dimension. Some
typical quality characteristics are given below.
Product characteristics
1. Accessibility Functionality Size
2. Availability Interchangeability Susceptibility
3. Appearance Maintainability Storability
4. Adaptability Odour – Strength
5. Cleanliness Operability -Taste
6. Consumption Portability – Testability
7. Durability Producibility Traceability
8. Disposability Reliability – Toxicity
9. Emittance Reparability Transportability
10. Flammability Safety – Vulnerability
11. Flexibility Security – Weight
Service quality characteristics
1. Accessibility Credibility – Honesty
2. Accuracy Dependability Promptness
3. Courtesy Efficiency – Responsiveness
4. Comfort Effectiveness Reliability
5. Competence Flexibility – Security
These are the characteristics that need to be specified and their achievement
controlled, assured, improved, managed and demonstrated. These are the
characteristics that form the subject matter of the product requirements
referred to in ISO 9000. When the value of these characteristics is quantified or
qualified they are termed product requirements. We used to use the term quality
requirements but this caused a division in thinking that resulted in people
regarding quality requirements as the domain of the quality personnel and
technical requirements being the domain of the technical personnel. All
requirements are quality requirements – they express needs or expectations that
are intended to be fulfilled by a process output that possesses inherent
characteristics. We can therefore drop the word quality. If a modifying word is
needed in front of the word requirements it should be a word that signifies the
subject of the requirements. Transportation system requirements would be
requirements for a transportation system, Audio speaker design requirements
would be requirements for the design of an audio speaker, component test
requirements would be requirements for testing components, and management
training requirements would be requirements for training managers. ISO 9000
requirements are often referred to as quality requirements as distinct from other
types of requirements but this is misleading. ISO 9000 is no more a quality
requirement than is ISO 1000 on SI units, ISO 2365 for Ammonium nitrate or
ISO 246 for Rolling Bearings. The requirements of ISO 9000 are quality
management system requirements – requirements for a quality management
system.
customer needs or achieve fitness for use is a quality characteristic. When
dealing with products the characteristics are almost always technical character-
istics, whereas service quality characteristics have a human dimension. Some
typical quality characteristics are given below.
Product characteristics
1. Accessibility Functionality Size
2. Availability Interchangeability Susceptibility
3. Appearance Maintainability Storability
4. Adaptability Odour – Strength
5. Cleanliness Operability -Taste
6. Consumption Portability – Testability
7. Durability Producibility Traceability
8. Disposability Reliability – Toxicity
9. Emittance Reparability Transportability
10. Flammability Safety – Vulnerability
11. Flexibility Security – Weight
Service quality characteristics
1. Accessibility Credibility – Honesty
2. Accuracy Dependability Promptness
3. Courtesy Efficiency – Responsiveness
4. Comfort Effectiveness Reliability
5. Competence Flexibility – Security
These are the characteristics that need to be specified and their achievement
controlled, assured, improved, managed and demonstrated. These are the
characteristics that form the subject matter of the product requirements
referred to in ISO 9000. When the value of these characteristics is quantified or
qualified they are termed product requirements. We used to use the term quality
requirements but this caused a division in thinking that resulted in people
regarding quality requirements as the domain of the quality personnel and
technical requirements being the domain of the technical personnel. All
requirements are quality requirements – they express needs or expectations that
are intended to be fulfilled by a process output that possesses inherent
characteristics. We can therefore drop the word quality. If a modifying word is
needed in front of the word requirements it should be a word that signifies the
subject of the requirements. Transportation system requirements would be
requirements for a transportation system, Audio speaker design requirements
would be requirements for the design of an audio speaker, component test
requirements would be requirements for testing components, and management
training requirements would be requirements for training managers. ISO 9000
requirements are often referred to as quality requirements as distinct from other
types of requirements but this is misleading. ISO 9000 is no more a quality
requirement than is ISO 1000 on SI units, ISO 2365 for Ammonium nitrate or
ISO 246 for Rolling Bearings. The requirements of ISO 9000 are quality
management system requirements – requirements for a quality management
system.
Quality Management
There are two schools of thought on quality management. One views quality management as the management of success and the other the elimination of failure. They are both valid. Each approaches the subject from a different angle:
The ‘success’ school is characterized by five questions :
1 What are you trying to do?
2 How do you make it happen?
3 How do you know it’s right?
4 How do you know it’s the best way of doing it?
5 How do you know it’s the right thing to do?
The ‘failure elimination’ school is characterized by five different questions
1 How do you know what is needed?
2 What could affect your ability to do it right?
3 What checks are made to verify achievement?
4 How do you ensure the integrity of these checks?
5 What action is taken to prevent a recurrence of failure?
In an ideal world, if we could design products, services and processes that could not fail we would have achieved the ultimate goal. Success means not only that products, services and processes fulfil their function but also that the function is what customers’ desire. Failure means not only that products, services and processes would fail to fulfil their function but also that their function was not what customers desired. A gold-plated mousetrap that does not fail is not a success if no one needs a gold-plated mousetrap.
The introductory clause of ISO 9001:1994 contained a statement that the aim of the requirements is to achieve customer satisfaction by prevention of nonconformities. (This was indicative of the failure school of thought.) The introductory clause of ISO 9001:2000 contains a statement that the aim is to enhance customer satisfaction through the effective application of the quality management system and the assurance of conformity to customer and applicable regulatory requirements. (This is indicative of the success school of thought.)
In reality you cannot be successful unless you know of the risks you are taking and plan to eliminate, reduce or control them. A unification of these approaches is what is therefore needed for organizations to achieve, sustain and improve quality. You therefore need to approach the achievement of quality from two different angles and answer two questions. What do we need
to do to succeed and what do we need to do to prevent failure?
Quality does not appear by chance, or if it does it may not be repeated. One has to design quality into the products and services. It has often been said that one cannot inspect quality into a product. A product remains the same after inspection as it did before, so no amount of inspection will change the quality of the product. However, what inspection does is measure quality in a way that allows us to make decisions on whether or not to release a piece of work. Work that passes inspection should be quality work but inspection unfortunately is not 100% reliable. Most inspection relies on human judgement and this can be affected by many factors, some of which are outside our control (such as the private life, health or mood of the inspector). We may also fail to predict the effect that our decisions have on others. Sometimes we go to great lengths in
preparing organization changes and find to our surprise that we neglected something or underestimated the effect of something. We therefore need other means to deliver quality products – we have to adopt practices that enable us to achieve our objectives while preventing failures from occurring.
The ‘success’ school is characterized by five questions :
1 What are you trying to do?
2 How do you make it happen?
3 How do you know it’s right?
4 How do you know it’s the best way of doing it?
5 How do you know it’s the right thing to do?
The ‘failure elimination’ school is characterized by five different questions
1 How do you know what is needed?
2 What could affect your ability to do it right?
3 What checks are made to verify achievement?
4 How do you ensure the integrity of these checks?
5 What action is taken to prevent a recurrence of failure?
In an ideal world, if we could design products, services and processes that could not fail we would have achieved the ultimate goal. Success means not only that products, services and processes fulfil their function but also that the function is what customers’ desire. Failure means not only that products, services and processes would fail to fulfil their function but also that their function was not what customers desired. A gold-plated mousetrap that does not fail is not a success if no one needs a gold-plated mousetrap.
The introductory clause of ISO 9001:1994 contained a statement that the aim of the requirements is to achieve customer satisfaction by prevention of nonconformities. (This was indicative of the failure school of thought.) The introductory clause of ISO 9001:2000 contains a statement that the aim is to enhance customer satisfaction through the effective application of the quality management system and the assurance of conformity to customer and applicable regulatory requirements. (This is indicative of the success school of thought.)
In reality you cannot be successful unless you know of the risks you are taking and plan to eliminate, reduce or control them. A unification of these approaches is what is therefore needed for organizations to achieve, sustain and improve quality. You therefore need to approach the achievement of quality from two different angles and answer two questions. What do we need
to do to succeed and what do we need to do to prevent failure?
Quality does not appear by chance, or if it does it may not be repeated. One has to design quality into the products and services. It has often been said that one cannot inspect quality into a product. A product remains the same after inspection as it did before, so no amount of inspection will change the quality of the product. However, what inspection does is measure quality in a way that allows us to make decisions on whether or not to release a piece of work. Work that passes inspection should be quality work but inspection unfortunately is not 100% reliable. Most inspection relies on human judgement and this can be affected by many factors, some of which are outside our control (such as the private life, health or mood of the inspector). We may also fail to predict the effect that our decisions have on others. Sometimes we go to great lengths in
preparing organization changes and find to our surprise that we neglected something or underestimated the effect of something. We therefore need other means to deliver quality products – we have to adopt practices that enable us to achieve our objectives while preventing failures from occurring.
Sunday, August 30, 2009
ISO 9001 / ISO 14001 Video
Watch ISO 14001 Video at http://www.youtube.com/watch?v=KUxbyQUGSnU
Watch ISO 9001 Video at http://www.youtube.com/watch?v=G8WI2MgyS7w
Watch ISO 9001 Video at http://www.youtube.com/watch?v=G8WI2MgyS7w
Measurement and Evaluation In ISO 14001:2004
After implementing the environmental policy, management needs to measure environmental that the data can be verified by an internal or external auditor.
interventions and their impact on the environment. This is done by building up an environmental effects register (environmental inventory). All equipment used for monitoring and measuring must be accurate and calibrated on a regular basis. To check the compliance status of an organization, additional information about regulations and other requirements is needed. A so called environmental regulations register?Eis often installed and maintained for this purpose. To obtain a better picture about the financial consequences of environmental protection, the accounting system should reflect environmental costs. Therefore, information about environmentally-induced costs and earnings needs to be collected. All this information should be recorded in such a manner.er
Environmental Performance Evaluation Accesses Environment Performance against environmental targets and objectives and against applicable environmental regulations. Responsibilities and authority need to be defined to deal with non-compliance within the EMS. This includes specifying the actions to be taken to correct an undesirable ituation and to prevent future non-compliance.
The analysis of environmental and economic performance leads to eco efficiency, the key component in sustainable business management.
The analysis of environmental and economic performance leads to eco
efficiency, the key component in sustainable business management. The recording of physical environmental data, environmental regulations and environmentally-induced financial information is necessary as a basis for effective decision making. Therefore, financial, legal and ecological data systems must be built up from scratch or adapted to the requirements of the EMS standard.
interventions and their impact on the environment. This is done by building up an environmental effects register (environmental inventory). All equipment used for monitoring and measuring must be accurate and calibrated on a regular basis. To check the compliance status of an organization, additional information about regulations and other requirements is needed. A so called environmental regulations register?Eis often installed and maintained for this purpose. To obtain a better picture about the financial consequences of environmental protection, the accounting system should reflect environmental costs. Therefore, information about environmentally-induced costs and earnings needs to be collected. All this information should be recorded in such a manner.er
Environmental Performance Evaluation Accesses Environment Performance against environmental targets and objectives and against applicable environmental regulations. Responsibilities and authority need to be defined to deal with non-compliance within the EMS. This includes specifying the actions to be taken to correct an undesirable ituation and to prevent future non-compliance.
The analysis of environmental and economic performance leads to eco efficiency, the key component in sustainable business management.
The analysis of environmental and economic performance leads to eco
efficiency, the key component in sustainable business management. The recording of physical environmental data, environmental regulations and environmentally-induced financial information is necessary as a basis for effective decision making. Therefore, financial, legal and ecological data systems must be built up from scratch or adapted to the requirements of the EMS standard.
Evaluation Of Compliance Of ISO 14001 EMS
The requirement to establish a procedure for periodically evaluating compliance with applicable legal and other requirements falls short of specifically requiring regulatory compliance audits but, in fact, a system of regular regulatory compliance audits may be the most practical means for meeting this requirement of the standard. In the U.S., determination of whether to conduct a compliance audit will be governed in part by the particular jurisdiction’s approach to allowing a legal privilege for the self-assessment audit.
Evaluation vs. Audit – The difference between an evaluation and audit can only be determined by looking outside of ISO 14001. Consulting a dictionary reveals that an evaluation involves a determination of value or worth and that an audit is an examination of accounts done by persons appointed for the purpose. A better definition `is the more specific ISO 19011:2002, Guidelines for Quality and/or Environmental Management Systems Auditing, which defines an audit as a “systematic, independent, and documented process for obtaining audit evidence and evaluating it objectively to determine the extent to which the audit criteria are fulfilled.” Many organizations do not have a system for evaluating regulatory compliance other than their own records and the inspections of regulatory officials. This lack of a verification system can be a risky way to operate. Reports of enforcement actions and consent agreements show that many organizations are blindsided by rogue employees who violate rules and falsify documents to cover up environmental misdeeds. Although ISO 14001 does not prescribe a specific approach to evaluation of regulatory compliance, organizations should consider methods for going beyond verification of records by collecting and evaluating physical evidence.
Evaluation vs. Audit – The difference between an evaluation and audit can only be determined by looking outside of ISO 14001. Consulting a dictionary reveals that an evaluation involves a determination of value or worth and that an audit is an examination of accounts done by persons appointed for the purpose. A better definition `is the more specific ISO 19011:2002, Guidelines for Quality and/or Environmental Management Systems Auditing, which defines an audit as a “systematic, independent, and documented process for obtaining audit evidence and evaluating it objectively to determine the extent to which the audit criteria are fulfilled.” Many organizations do not have a system for evaluating regulatory compliance other than their own records and the inspections of regulatory officials. This lack of a verification system can be a risky way to operate. Reports of enforcement actions and consent agreements show that many organizations are blindsided by rogue employees who violate rules and falsify documents to cover up environmental misdeeds. Although ISO 14001 does not prescribe a specific approach to evaluation of regulatory compliance, organizations should consider methods for going beyond verification of records by collecting and evaluating physical evidence.
Thursday, August 27, 2009
Basic QC and Six Sigma Tools
The 7 QC Tools
The Seven Quality Control tools (7QC tools) are graphical and statistical tools which are most often used in QC for continuous improvement. Since they are so widely utilized by almost every level of the company, they have been nicknamed the Magnificent Seven. They are applicable to improvements in all dimensions of the process performance triangle: variation of quality, cycle time and yield of productivity.
Each one of the 7QC tools had been used separately before 1960. However, in the early 1960s, they were gathered together by a small group of Japanese scientists lead by Kaoru Ishikawa, with the aim of providing the QC Circles with effective and easy-to-use tools. They are, in alphabetical order, cause-and-effect diagram, check sheet, control chart, histogram, Pareto chart, scatter diagram and stratification. In Six Sigma, they are extensively used in all phases of the improvement methodology – define, measure, analyze, improve and control.
(1) Cause-and-effect diagram
An effective tool as part of a problem-solving process is the cause-and-effect diagram, also known as the Ishikawa diagram (after its originator) or fishbone diagram. This technique is useful to trigger ideas and promote a balanced approach in group brainstorming sessions where individuals list the perceived sources (causes) with respect to outcomes (effect).
When constructing a cause-and-effect diagram, it is often appropriate to consider six main causes that can contribute to an outcome response (effect): so-called 5M1E (man, machine, material, method, measurement, and environment).
When preparing a cause-and-effect diagram, the first step is to agree on the specific wording of the effect and then to identify the main causes that can possibly produce the effect. The main causes can often be identified as any of 5M1E, which helps us to get started, but these are by no means exhaustive.
Using brainstorming techniques, each main cause is analyzed. The aim is to refine the list of causes in greater detail until the root causes of that particular main cause are established. The same procedure is then followed for each of the other main causes. The method is a main cause, the pressure and the temperature are the causes, and “the pressure is low” and “the temperature is too high” are the root causes.
(2) Check sheet
The check sheet is used for the specific data collection of any desired characteristics of a process or product that is to be improved. It is frequently used in the measure phase of the Six Sigma improvement methodology, DMAIC. For practical purposes, the check sheet is commonly formatted as a table. It is important that the check sheet is kept simple and that its design is aligned to the characteristics that are measured. Consideration should be given as to who should gather the data and what measurement intervals to apply. For example, Figure 4.2 shows a check sheet for defect items in an assembly process of automobile ratios.
(3) Control chart
(a) Introduction
The control chart is a very important tool in the “analyze, improve and control” phases of the Six Sigma improvement methodology. In the “analyze” phase, control charts are applied to judge if the process is predictable; in the “improve” phase, to identify evidence of special causes of variation so that they can be acted on; in the “control” phase, to verify that the performance of the process is under control.
The original concept of the control chart was proposed by Walter A. Shewhart in 1924 and the tool has been used extensively in industry since the Second World War, especially in Japan and the USA after about 1980. Control charts offer the study of variation and its source. They can give process monitoring and control, and can also give direction for improvements. They can separate special from common cause issues of a process. They can give early identification of special causes so that there can be timely resolution before many poor quality products are produced. Shewhart control charts track processes by plotting data over time in the form shown in Figure 4.3. This chart can track either variables or attribute process parameters. The types of variable charts are process mean (x), range (R), standard deviation (s), individual value (x) and moving range (Rs). The attribute types are fraction nonconforming (p), number of nonconforming items (np), number of nonconformities (c), and nonconformities per unit (u).
(4) Histogram
It is meaningful to present data in a form that visually illustrates the frequency of occurrence of values. In the analysis phase of the Six Sigma improvement methodology, histograms are commonly applied to learn about the distribution of the data within the results Ys and the causes Xs collected in the measure phase and they are also used to obtain an understanding of the potential for improvements.
(5) Pareto chart
The Pareto chart was introduced in the 1940s by Joseph M.Juran, who named it after the Italian economist and statistician Vilfredo Pareto, 1848–1923. It is applied to distinguish the “vital few from the trivial many” as Juran formulated the purpose of the Pareto chart. It is closely related to the so-called 80/20 rule – “80% of the problems stem from 20% of the causes,” or in Six Sigma terms “80% of the poor values in Y stem from 20% of the Xs.”
In the Six Sigma improvement methodology, the Pareto chart has two primary applications. One is for selecting appropriate improvement projects in the define phase. Here it offers a very objective basis for selection, based on, for example, frequency of occurrence, cost saving and improvement potential in process performance.
The other primary application is in the analyze phase for identifying the vital few causes (Xs) that will constitute the greatest improvement in Y if appropriate measures are taken.
A procedure to construct a Pareto chart is as follows:
1) Define the problem and process characteristics to use in the diagram.
2) Define the period of time for the diagram – for example, weekly, daily, or shift.
Quality improvements over time can later be made from the information determined within this step.
3) Obtain the total number of times each characteristic occurred.
4) Rank the characteristics according to the totals from
(6) Scatter diagram
The scatter plot is a useful way to discover the relationship between two factors, X and Y, i.e., the correlation. An important feature of the scatter plot is its visualization of the correlation pattern, through which the relationship can be determined. In the improve phase of the Six Sigma improvement methodology, one often searches the collected data for Xs that have a special influence on Y. Knowing the existence of such relationships, it is possible to identify input variables that
cause special variation of the result variable. It can then be determined how to set the input variables, if they are controllable, so that the process is improved. When several Xs may influence the values of Y, one scatter plot should be drawn for each combination of the Xs and Y.
(7) Stratification
Stratification is a tool used to split collected data into subgroups in order to determine if any of them contain special cause variation. Hence, data from different sources in a process can be separated and analyzed individually. Stratification is mainly used in the analyze phase to stratify data in the
search for special cause variation in the Six Sigma improvement methodology.
The most important decision in using stratification is to determine the criteria by which to stratify. Examples can be machines, material, suppliers, shifts, day and night, age groups and so on. It is common to stratify into two groups. If the number of observations is large enough, more detailed stratification is also possible.
The Seven Quality Control tools (7QC tools) are graphical and statistical tools which are most often used in QC for continuous improvement. Since they are so widely utilized by almost every level of the company, they have been nicknamed the Magnificent Seven. They are applicable to improvements in all dimensions of the process performance triangle: variation of quality, cycle time and yield of productivity.
Each one of the 7QC tools had been used separately before 1960. However, in the early 1960s, they were gathered together by a small group of Japanese scientists lead by Kaoru Ishikawa, with the aim of providing the QC Circles with effective and easy-to-use tools. They are, in alphabetical order, cause-and-effect diagram, check sheet, control chart, histogram, Pareto chart, scatter diagram and stratification. In Six Sigma, they are extensively used in all phases of the improvement methodology – define, measure, analyze, improve and control.
(1) Cause-and-effect diagram
An effective tool as part of a problem-solving process is the cause-and-effect diagram, also known as the Ishikawa diagram (after its originator) or fishbone diagram. This technique is useful to trigger ideas and promote a balanced approach in group brainstorming sessions where individuals list the perceived sources (causes) with respect to outcomes (effect).
When constructing a cause-and-effect diagram, it is often appropriate to consider six main causes that can contribute to an outcome response (effect): so-called 5M1E (man, machine, material, method, measurement, and environment).
When preparing a cause-and-effect diagram, the first step is to agree on the specific wording of the effect and then to identify the main causes that can possibly produce the effect. The main causes can often be identified as any of 5M1E, which helps us to get started, but these are by no means exhaustive.
Using brainstorming techniques, each main cause is analyzed. The aim is to refine the list of causes in greater detail until the root causes of that particular main cause are established. The same procedure is then followed for each of the other main causes. The method is a main cause, the pressure and the temperature are the causes, and “the pressure is low” and “the temperature is too high” are the root causes.
(2) Check sheet
The check sheet is used for the specific data collection of any desired characteristics of a process or product that is to be improved. It is frequently used in the measure phase of the Six Sigma improvement methodology, DMAIC. For practical purposes, the check sheet is commonly formatted as a table. It is important that the check sheet is kept simple and that its design is aligned to the characteristics that are measured. Consideration should be given as to who should gather the data and what measurement intervals to apply. For example, Figure 4.2 shows a check sheet for defect items in an assembly process of automobile ratios.
(3) Control chart
(a) Introduction
The control chart is a very important tool in the “analyze, improve and control” phases of the Six Sigma improvement methodology. In the “analyze” phase, control charts are applied to judge if the process is predictable; in the “improve” phase, to identify evidence of special causes of variation so that they can be acted on; in the “control” phase, to verify that the performance of the process is under control.
The original concept of the control chart was proposed by Walter A. Shewhart in 1924 and the tool has been used extensively in industry since the Second World War, especially in Japan and the USA after about 1980. Control charts offer the study of variation and its source. They can give process monitoring and control, and can also give direction for improvements. They can separate special from common cause issues of a process. They can give early identification of special causes so that there can be timely resolution before many poor quality products are produced. Shewhart control charts track processes by plotting data over time in the form shown in Figure 4.3. This chart can track either variables or attribute process parameters. The types of variable charts are process mean (x), range (R), standard deviation (s), individual value (x) and moving range (Rs). The attribute types are fraction nonconforming (p), number of nonconforming items (np), number of nonconformities (c), and nonconformities per unit (u).
(4) Histogram
It is meaningful to present data in a form that visually illustrates the frequency of occurrence of values. In the analysis phase of the Six Sigma improvement methodology, histograms are commonly applied to learn about the distribution of the data within the results Ys and the causes Xs collected in the measure phase and they are also used to obtain an understanding of the potential for improvements.
(5) Pareto chart
The Pareto chart was introduced in the 1940s by Joseph M.Juran, who named it after the Italian economist and statistician Vilfredo Pareto, 1848–1923. It is applied to distinguish the “vital few from the trivial many” as Juran formulated the purpose of the Pareto chart. It is closely related to the so-called 80/20 rule – “80% of the problems stem from 20% of the causes,” or in Six Sigma terms “80% of the poor values in Y stem from 20% of the Xs.”
In the Six Sigma improvement methodology, the Pareto chart has two primary applications. One is for selecting appropriate improvement projects in the define phase. Here it offers a very objective basis for selection, based on, for example, frequency of occurrence, cost saving and improvement potential in process performance.
The other primary application is in the analyze phase for identifying the vital few causes (Xs) that will constitute the greatest improvement in Y if appropriate measures are taken.
A procedure to construct a Pareto chart is as follows:
1) Define the problem and process characteristics to use in the diagram.
2) Define the period of time for the diagram – for example, weekly, daily, or shift.
Quality improvements over time can later be made from the information determined within this step.
3) Obtain the total number of times each characteristic occurred.
4) Rank the characteristics according to the totals from
(6) Scatter diagram
The scatter plot is a useful way to discover the relationship between two factors, X and Y, i.e., the correlation. An important feature of the scatter plot is its visualization of the correlation pattern, through which the relationship can be determined. In the improve phase of the Six Sigma improvement methodology, one often searches the collected data for Xs that have a special influence on Y. Knowing the existence of such relationships, it is possible to identify input variables that
cause special variation of the result variable. It can then be determined how to set the input variables, if they are controllable, so that the process is improved. When several Xs may influence the values of Y, one scatter plot should be drawn for each combination of the Xs and Y.
(7) Stratification
Stratification is a tool used to split collected data into subgroups in order to determine if any of them contain special cause variation. Hence, data from different sources in a process can be separated and analyzed individually. Stratification is mainly used in the analyze phase to stratify data in the
search for special cause variation in the Six Sigma improvement methodology.
The most important decision in using stratification is to determine the criteria by which to stratify. Examples can be machines, material, suppliers, shifts, day and night, age groups and so on. It is common to stratify into two groups. If the number of observations is large enough, more detailed stratification is also possible.
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