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Below are key definitions for frequently used Lean Six Sigma terminology

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  • Affinity Diagram – A technique for organizing individual pieces of information into groups or broader categories.
  • ANOVA – Analysis of Variance. A statistical test for identifying significant differences between process or system treatments or conditions. It is done by comparing the variances around the means of the conditions being compared.
  • Attribute Data – Data which on one of a set of discrete values such as pass or fail, yes or no.
  • Average – Also called the Mean, it is the arithmetic average of all of the sample values. It is calculated by adding all of the sample values together and dividing by the number of elements (n) in the sample.


  • Bar Chart – A graphical method which depicts how data falls into different categories.
  • Benchmarking – The comparison of an organisation’s measures with similar measures in other organisations. Shows gaps for improvement.
  • Black Belt – A person who receives approximately four weeks training in DMAIC, analytical problem solving and change management methods. A Black Belt is a full time Six Sigma team leader solving problems under the direction of a Champion.


  • Capability – A comparison of the required operation width of a process or system to its actual performance width. Expressed as a percentage (yield), a defect rate (dpm, dpmo,), an index (Cp, Cpk, Pp, Ppk), or as a sigma score (Z).
  • Cause and Effect Diagram – A pictorial diagram in the shape of a fishbone showing all possible variables that could affect a given process output measure.
  • Central Tendency – A measure of the point about which a group of values is clustered; two measures of central tendency are the Mean and the Median.
  • Champion – A Champion recognizes, defines, assigns and supports the successful completion of Six Sigma projects; they are accountable for the results of the project and the business roadmap to achieve Six Sigma performance within their span of control.
  • Change Management – Is defined as being the processes and actions to take into account all human and social aspects of the change from the launch of the project to its end.
  • Characteristic – A process input or output which can be measured and monitored.
  • Common Causes of Variation – Those sources of variability in a process which are truly random, i.e., inherent in the process itself. Always present, predictable and expected.
  • Complexity – The level of difficulty to build, solve or understand something based on the number of inputs, interactions and uncertainty involved.
  • Continuous Data – Also known as variable, quantitative or measurable data. Data that can take any value i.e. can be to any degree of accuracy. Can be measured on a scale and compared with, added to or subtracted from other continuous data of the same type e.g. weight, pressure, cost etc.
  • Control Chart – The most powerful tool of Statistical Process Control. It consists of a Run Chart, together with statistically determined Upper and Lower Control Limits and a Center Line.
  • Control Limits – Upper and lower bounds in a Control Chart that are determined by the process itself. They can be used to detect Special or Common Causes of variation. They are usually set at ±3 Standard Deviations from the central tendency.
  • Correlation Coefficient – A measure of the linear relationship between two variables.
  • Cost of Poor Quality (COPQ) – The costs associated with any activity that is not doing the right thing right the first time. It is the financial qualification any waste that is not integral to the product or service.
  • Cp – A capability measure defined as the ratio of the specification width to short-term process performance width.
  • CPk – An adjusted short-term capability index that reduces the capability score in proportion to the offset of the process center from the specification target.
  • Critical to Quality – Any characteristic that is critical to the perceived quality of the product, process or system. See Significant Y.
  • Critical X – An input to a process or system that exerts a significant influence on any one or all of the key outputs of a process.
  • Customer – Anyone who uses or consumes a product or service, whether internal or external to the providing organization or provider.
  • CuSum Charts – Statistical method (Cumulative Sum). These detect process changes more sensitively.
  • Cycle Time – The total amount of elapsed time expended from the time a task, product or service is started until it is completed.


  • Defect – An output of a process that does not meet a defined specification, requirement or desire such as time, length, color, finish, quantity, temperature etc. Also includes anything not done right the first time.
  • Defective – A unit of product or service that contains at least one defect.
  • Defect Opportunity – Any event which can be measured that provides a chance of not meeting a Value Requirement.
  • Design of Experiements – Generally, it is the discipline of using an efficient, structured, and proven approach to interrogating a process or system for the purpose of maximizing the gain in process or system knowledge.
  • Design for Six Sigma (DFSS) – The use of Lean Six Sigma thinking, tools and methods applied to the design of products and services to improve the initial release performance, ongoing reliability, and life-cycle cost.
  • Discrete Data – Any data that is not continuous. Can only have a finite set of values. Can be counted and has whole numbers (Integers).
  • DMAIC – The acronym for core phases of the Lean Six Sigma methodology used to solve process and business problems through data and analytical methods.
  • DPMO – Defects per Million Opportunities. The total number of defects observed divided by the total number of opportunities, expressed in parts per million. Sometimes called Defects per Million (DPM).
  • DPU – The total number of defects detected in some number of units divided by the total number of those units.


  • Error-proofing methods – 4 Main methods according to Shingo: Elimination, Flagging, Facilitation, Mitigation.
  • Experimental DesignSee Design of Experiments.


  • Failure Mode and Effects Analysis (FMEA) – A procedure used to identify, assess and mitigate risks associated with potential product, system or process Failure Modes.
  • FIFO – First In First Out priciple.
  • Final Yield (FY) – Yield at the end of the process excluding scrap.
  • Fishbone DiagramSee Cause and Effect Diagram.
  • Five S’s (Lean Principle)
    • Sorting – Selecting or separating
    • Simplifying – Straighten and store
    • Sweeping – Scrub and shine
    • Standardizing
  • Five Why’s – This is a root cause analysis method achieved by asking WHY in response to a problem statement until a root cause is found and a solution is suggested.
  • Flowchart – A graphic model of the flow of activities, material and/or information that occurs during a process.
  • Force Field Analysis – A graphical method for comparing the forces for and against change – the positive and negative.
  • Frame – A frame is a limited description of a problem that filters what is relevant.


  • Gauge R&RS – Quantitative assessment of how much variation (repeatability and reproducibility) is in a measurement system compared to the total variation of the process or system.
  • Green Belt – A person who receives approximately two weeks of training in DMAIC, analytical problem solving and change management methods. A Green Belt is a part time Lean Six Sigma position that applies Lean Six Sigma to their local area, doing smaller-scoped projects and providing support to Black Belt projects.


  • Handsoff – Where an item or service is passed across the boundary between two distinct organisational functions inside or outside the organisation.
  • Hidden Factory or Operation – All the activities that occur because processes are not right first time. Not added separately into the cost of goods and therefore not known by management.
  • Histogram – A bar chart which shows the frequency distribution of the data.


  • ICOR Chart – Inputs, Constraints, Outputs, Resources. ICOR, derived from IDEFO, is a top down method and uses simple rules to ensure clarity of the definitions.
  • Implementation Team – A cross-functional executive team representing various areas of the company. Its charter is to drive the implementation of Lean Six Sigma by defining and documenting practices, methods and operating policies.
  • Input – A resource consumed, utilized or added to a process or system. Synonymous with X, characteristic, and input variable.
  • Input-Process-Output (IPO) Diagram – A visual representation of a process or system where inputs are represented by input arrows to a box (representing the process or system) and outputs are shown using arrows emanating out of the box.
  • Isikawa DiagramSee Cause and Effect Diagram and Fishbone Diagram.



  • KOMY – Key Output Measure Y
  • Kano Model – A model/diagram used to analyse what is delivered to the customer in terms of 1) basics, 2) performance items, 3) ‘delighters’. It helps think about customer expectations.


  • Lean Six Sigma – The combination of the methods, tools and philosophies of Lean Thinking and Six Sigma. The two toolkits are largely complementary.
  • Lean Systems – Lean systems display the following characteristics:
    • The elimination of non-value adding activity (TIME)
    • Only producing what is required and when it’s required
    • Close links in the value chain including supply chain inputs (JIT)
    • Doing things right first time
    • Ensuring processes are robust
  • Least Squares – A method of curve-fitting that defines the best fit as the one that minimizes the sum of the squared deviations of the data points from the fitted curve.
  • Long-Term Variation – The observed variation of an input or output characteristic which has had the opportunity to experience the majority of the variation effects that influence it.
  • Lower Control Limit (LCL) – Used with Control Charts: the limit above which the subgroup statistics must remain for the process to be in control. Typically, 3 Standard Deviations below the central tendency.
  • Lower Specification Limit – The lowest value of a characteristic which is acceptable.


  • Master Black Belt – A person who has received training beyond a Black Belt. The technical, go-to expert regarding technical and project issues in Lean Six Sigma. Master Black Belts teach and mentor other Belts, their projects and support Champions.
  • MeanSee Average.
  • Measurement – The act of obtaining knowledge about an event or characteristic through measured quantification or assignment to categories.
  • Measurement Accuracy – For a repeated measurement, it is a comparison of the average of the measurements compare to some known standard.
  • Measurement Precision – For a repeated measurement, it is the amount of variation that exists in the measured values.
  • Measurement Systems Analysis (MSA) – An assessment of the accuracy and precision of a method of obtaining measurements. See also Gauge R&R.
  • Median – The middle value of a data set when the values are arranged in either ascending or descending order.
  • Metric – A measure that is considered to be a key indicator of performance. It should be linked to goals or objectives and carefully monitored.
  • Mistake Proofing – Error proofing. Poka Yoke.
  • Moving Range Chart (MR) – Used to obtain an estimate of the spread of data


  • Natural Tolerances of a ProcessSee Control Limits.
  • Nominal Group Technique – A structured method that a team can use to generate and rank a list of ideas or items.
  • Non-Value Added (NVA) – Any activity performed in producing a product or delivering a service that does not add value, where value is defined as changing the form, fit or function of the product or service and is something for which the customer is willing to pay.
  • Normal Distribution – The distribution characterized by the smooth, bell-shaped curve. Synonymous with Gaussian Distribution.
  • Normalised Yield (NY) – Is the average yield per process step or opportunity.
  • np Chart – A type of control chart which monitors the proportion of defectives in constant samples.
    • n – number of items in the sample,
    • p – proportion defective (as a decimal)


  • Objective Statement – A succinct statement of the goals, timing and expectations of a Lean Six Sigma improvement project.
  • Operational Definition – Is a clear, concise description of a measurement and the process by which it is to be collected.
  • Opportunities – The number of characteristics, parameters or features of a product or service that can be classified as acceptable or unacceptable.
  • Out of Control – A process is said to be out of control if it exhibits variations larger than its Control Limits or shows a pattern of variation.
  • Output – The product or services produces by a process step. May be physical, information or human. A resource or item or characteristic that is the product of a process or system. See also Y, CTQ.
  • Output Characteristics – What you must focus on to measure your performance.


  • Pareto Chart – A Bar Chart for Attribute (or categorical) Data categories presented in descending order of frequency.
  • Pareto Principle – The general principle originally proposed by Vilfredo Pareto (1848-1923) that the majority of influence on an outcome is exerted by a minority of input factors. Sometimes also refered to as the 80/20 Rule.
  • PDCA – Plan, Do, Check, Act an improvement methodology.
  • Poka-Yoke – A translation of a Japanese term meaning to mistake-proof.
  • Policy – A framework of direction & guidance for a process
  • Prioritisation Matrix – A team tool matrix method to analyse priorities for project selection and/or action.
  • Probability – The likelihood of an event or circumstance occurring.
  • Problem Satement – A succinct statement of a business situation which is used to bound and describe the problem the Lean Six Sigma project is attempting to solve.
  • Procedure – A description of how a process or parts of a process is managed and operated.
  • Process – A structured set of activities that transform a set of inputs into specified outputs that provide value to customers and stakeholders.
  • Process Capability – It is a means of establishing the extent a process is likely to produce items acceptable to the design i.e. within specified tolerances.
  • Process Characterization – The act of thoroughly understanding a process, including the specific relationship(s) between its outputs and the inputs, and its performance and capability.
  • Process Flow DiagramSee Flowchart.
  • Process Mapping – Process Mapping is a diagrammatic representation of the operation of a process. Process Mapping is essential for process improvement, and is a picture of how things happen.
  • Process Owner – Process Owners have responsibility for process performance and resources. They provide support, resources and functional expertise to Lean Six Sigma projects. They are accountable for implementing developed Lean Six Sigma solutions into their process.
  • Process Sigma – A measurement scale that compares the output of a process (Key Output Measure Y) to the Value requirements (Performance Standards).


  • Quality – Uniformity around a target value
  • Quality Function Deployment (QFD) – A systematic process used to integrate customer requirements into every aspect of the design and delivery of products and services.


  • RACI Charting – A simple method of managing who does what for routine activities. Table is filled in with names against – R: Responsible; A: Accountable; C: Consulted and I: Informed. Every name must have only one ‘A’.
  • RAG Colour Coding – Red, Amber and Green – visual performance trends.
  • Range – A measure of the variability in a data set. It is the difference between the largest and smallest values in a data set.
  • Regression Analysis – A statistical technique for determining the mathematical relation between a measured quantity and the variables it depends on. Includes Simple and Multiple Linear Regression.
  • Relations Diagram – It helps to see relationships between issues.
  • Repeatability – The extent to which repeated measurements of a particular object with a particular instrument produce the same value. See also Gauge R&R.
  • Reproducibility – The extent to which repeated measurements of a particular object with a particular individual produce the same value. See also Gauge R&R.
  • Rework – Activity required to correct defects produced by a process.
  • Risk Priority Number – The aggregate score of a failure mode including its severity, frequency of occurrence and ability to be detected.
  • Rolled Throughput Yield – The probability of a unit going through all process steps or system characteristics with zero defects. Product of throughput yields across the entire process.
  • Run Chart – A basic graphical tool that charts a characteristics performance over time.


  • Scatter Plot – A chart in which one variable is plotted against another to determine the relationship, if any, between the two.
  • Short Term Variation – The amount of variation observed in a characteristic which has not had the opportunity to experience all the sources of variation from the inputs acting on it.
  • Sigma Score (Z) – A commonly used measure of process capability that represents the number of short-term Standard Deviations between the Center of a process and the closest specification limit. Sometimes referred to as sigma level, or simply Sigma.
  • Significant Y – An output of a process that exerts a significant influence on the success of the process or the customer.
  • SIPOC – The SIPOC is a High Level Process map identifying Suppliers, Input, Process, Output and Customers.
  • Six M’s – Variation elements in processes: Man, Machine, Material, Method, Measurement, Mother nature.
  • Six Sigma – This is seen as many things: A business philosophy to enable Culture Change; A Systematic Process/Methodology for Improvement; A standard Measure of Performance; A series of Questions and Prompts; A collection of Supporting Tools & Techniques; A catalyst for Change Efforts.
  • Six Sigma Leader – A person who leads the implementation of Lean Six Sigma; coordinates all of the necessary activities, assures optimal results are obtained and keeps everyone informed of progress made.
  • Six Sigma Project – A well defined effort that states a business problem in quantifiable terms and with known improvement expectations.
  • Six Sigma Quality – Fewer than 3.4 DPMO.
  • SMART – An acronym to help evaluate a Problem Statement in terms of it being Specific, Measurable, Achievable, Relevant, Timebound.
  • Special Cause Variation – Causes a process to go out of control, as typically seen on a control chart. Unpredictable and unexpected.
  • Specification Limits – The bounds of acceptable performance for a characteristic.
  • Stability (of a process) – A process is said to be stable if it shows no recognizable pattern of change and no Special Causes of variation are present.
  • Stakeholder Analysis – Stakeholder analysis is a term that refers to the action of analysing the attitudes of stakeholders towards something (most frequently a project). It is frequently used during the preparation phase of a project to assess the attitudes of the stakeholders regarding the potential changes.
  • Stakeholder Mapping – A demonstrable analysis of Synergy (common goal) versus Antagonism (personal game).
  • Standard Deviation – One of the most common measures of variability in a data set or in a population. It is the square root of the variance.
  • Statistical Problem – A problem that is addressed with facts and data analysis methods.
  • Statistical Process Control (SPC) – The use of basic graphical and statistical methods for measuring, analysing and controlling the variation of a process for the purpose of continuously improving the process. A process is said to be in a state of statistical control when it exhibits only random variation.
  • Statistical Solution – A data driven solution with known confidence/risk levels, as opposed to a qualitative, “I think” solution.
  • Stratification – Can also be known as segmentation. The division of a data set by separating it into categories.
  • Supplier – A person or entity responsible for providing an input to a process in the form of resources or information.


  • Taguchi Method – A design of experiments which aims to find how to set up processes that produce quality product whilst being insensitive to variations in the input variables.
  • Throughput Yield (TPY) – TPY = Units Through the Process, Right The First Time/Units Submitted.
  • Tollgate – End of phase.
  • TOPS-8D – Team-Orientated Problem Solving – 8 Disciplines.
  • Trend – A gradual, systematic change over time or some other variable.
  • Tree Diagram – A graphical depiction of how a single topic or task can be broken down into a hierarchy of sub-topics or sub-tasks.


  • Upper Control Limit (UCL) for Control Charts – The Upper Limit below which a process statistic must remain to be in Control. Typically this value is 3 Standard Ddeviations above the central tendency.
  • Upper Specification Limit (USL) – The highest value of a characteristic which is acceptable.


  • Value Stream Mapping – A high level graphical description of the steps between the start and finish of a process. It includes physical (material) and information flows.
  • Variability – A generic term that refers to the property of a characteristic, process or system to take on different values when it is repeated.
  • Variables – Quantities which are subject to change or variability.
  • Variable Data – Data which is Continuous, which can be meaningfully subdivided, i.e. can have decimal subdivisions.
  • Variance – A specifically defined mathematical measure of variability in a data set or population. It is the square of the Standard Deviation.
  • VariationSee Variability.
  • Visual Management – The use of visible graphs, charts, inventory arrangements, and storage methods that aid in implementing and maintaining lean manufacturing within a plant. An excellent communication means.
  • VOB – Voice of the Business. Represents the needs of the business and the key stakeholders of the business. It is usually items such as profitability, revenue, growth, market share, etc.
  • VOC – Voice of the Customer. Represents the expressed and non-expressed needs, wants and desires of the recipient of a process output, a product or a service. It is usually expressed as specifications, requirements or expectations.
  • VOP – – Voice of the Process. Represents the performance and capability of a process to achieve both business and customer needs. It is usually expressed in some form of an efficiency and/or effectiveness metric.



  • X – An input characteristic to a process or system. In Lean Six Sigma it is usually used in the expression of Y=f(X), where the output (Y) is a function of the inputs (X).


  • Yellow Belt – A person who receives approximately one week of training in problem solving and process optimization methods. Yellow Belts participate in Process Management activates, participate on Green and Black Belt projects and apply concepts to their work area and their job.


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