Glossary of Lean and Six Sigma Terms - Paloma Consulting Limited

7 QC - Tools Used by Japanese Quality Circles, a set of quantitative improvement tools including Flow Charts, Check sheets, Histograms, Pareto Charts, Scatter plots, Cause and Effect diagrams and Statistical Process Control Charts.

7 Wastes - Originally defined as part of the Toyota Production System – Transportation, Inventory, unnecessary Motion, Waiting, Over-Production, Over-Processing, Defects and rework. (TIMWOOD)

Alpha Risk - The probability of accepting the alternate hypothesis when, in reality, the null hypothesis is true.

Alternative Hypothesis - A tentative explanation which indicates that an event does not follow a chance distribution; a contrast to the null hypothesis.

Analysis of Variance (ANOVA) - A statistical method for evaluating the effect that factors have on process mean and for evaluating the differences between the means of two or more normal distributions.

Andon - A signal light used to alert workers to problems.

APQP - Advanced Product Quality Planning. A quality assurance procedure used in the automotive industry to certify supplier production of new components

Assignable Cause - A process input variable that can be identified and that contributes in an observable manner to non-random shifts in process mean and/or standard deviation.

Attribute Data - Quality data that typically reflects the number of conforming or non-conforming units or the number of non-conformities per unit on a go/no go or accept/reject basis.

Autonomous Maintenance - A Total Productive Maintenance (TPM) process to restore deteriorated equipment and develop operator maintenance standards.

Average - Sum of all measurements divided by the total number of measurements. Statistic which is used to estimate the population mean.

Benchmarking - A process for identification of external best-in-class practices and standards for comparison against internal practices.

Beta Risk - The probability of accepting the null hypothesis when, in reality, the alternate hypothesis is true.

Binomial Distribution - A statistical distribution associated with data that is one of two possible states such as Go-No Go or Pass-Fail.

Black Belt - A process improvement project team leader who is trained and certified in Six Sigma methodology and tools and who is responsible for successful project execution.

Brainstorming - A team-oriented approach used in problem solving to develop a list of possible causes that may be linked to an observed effect.

Breakdown Maintenance - The practice of only maintaining equipment when it fails.

C Charts - Charts which display the number of defects per sample. Used where sample size is constant.

Capability Indices - A mathematical calculation used to compare the process variation to a specification.

Cause - That which produces an effect or brings about a change.

Cause and Effect (C&E) Diagram - One of the seven basic tools for problem solving and is sometimes referred to as a "fishbone" diagram because of its structure. The head represents the "effect" and the major legs of the structure are the "cause categories.” The substructure represents the list of potential causes which can induce the "effect."

Centre line - The line on a statistical process control chart which represents the process mean.

Central Tendency - Numerical average, e.g., mean, median, and mode; centre line on a statistical process control chart.

Champion - A business leader who not only supports projects but can also lead, implement and deploy the Six Sigma philosophy.

Characteristic - A definable or measurable feature of a process, product, or service.

Chronic Losses - Fundamental but unseen deterioration of equipment which combine to produce Sporadic Losses (Breakdowns)

CI (Continuous Improvement) - Continuous Improvement. The practice of engaging all staff in small incremental improvement activities in their work areas.

Classification - Differentiation of variables.

Common Cause - An inherent natural source of variation.

Condition Based Maintenance - Using technologies such as Thermography, Vibration Analysis and Oil Debris Analysis to predict impending failure and perform maintenance accordingly.

Confidence Interval - The interval width between the upper and lower confidence limits.

Confidence Limits - The two values that define the confidence interval.

Confounding - Allowing two or more variables to vary together so that it is impossible to separate their unique effects.

Consumer Risk - Probability of accepting a lot when, in fact, the lot should have been rejected (see beta risk).

Continuous Data - Data obtained from a measurement system which has an infinite number of possible outcomes.

Continuous Improvement (CI) - The practice of engaging all staff in small incremental improvement activities in their work areas.

Control Chart - A graphical chart of a characteristic's performance across time in relation to its natural limits and central tendency.

Control Limits - Apply to all control charts and are used to determine the state of statistical control. Control limits are derived statistically and are not related to specification limits in any way.

Control Plan - A formal quality document that describes all of the elements required to control variations in a particular process.

Corrective Maintenance - Using historic failure data to make Preventive Maintenance more effective.

Correlation - The relationship between two sets of data such that when one changes, the other is likely to make a corresponding change. Also, a statistical tool for determining the relationship between two sets of data.

Cost Of Poor Quality (COPQ) - Cost associated with providing poor quality products or services. Can be divided into five cost categories: Prevention, Appraisal, Internal failure, External failure and Waste. Scrap and rework are examples of Internal failure. Warranty costs are an example of external failure after delivery of the product or service.

Critical to Quality Characteristic (CTQ) - A characteristic determined to be important in the eyes of the customer.

Data - Factual information used as a basis for reasoning, discussion, or calculation.

Data Transformation - A mathematical technique used to transform the shape of any distribution.

Defect - Any product characteristic that deviates outside of specification limits that is likely to cause customer dissatisfaction.

Defects per Million Opportunities (DPMO) - Quality metric used in the Six Sigma process and is calculated by the number of defects observed divided by the number of opportunities for defects normalised to 1 million units.

Design Failure Modes Effect Analysis (DFMEA) - The technique identifies and documents potential failure modes and numerically identifies the risk of new product features failing in terms of the severity, probability of occurrence and detectability.

DMADV - Define, Measure, Analyse, Design (a new process), Verify (that it works) - the Six Sigma methodology for new processes.

DMAIC - Define, Measure, Analyse, Improve, Control – the Six Sigma methodology for existing processes.

DoE - Design of Experiments. A technique for testing the effect on the output of a process by changing more than one input variable at the same time.

Error Proofing - Using devices which ensure an error cannot be made.

Failure Modes and Effects Analysis (FMEA) - The technique identifies and documents potential failure modes and numerically identifies the risk in terms of the severity, probability of occurrence and detectability. It can be applied to any process, design or system.

FIFO - First In First Out. A method to ensure that parts are used in the order in which they are produced.

First Time Yield (FTY) - The yield of any process step that occurs without the need for any rework.

Gauge Accuracy - The average difference observed between a gauge under evaluation and a master gauge when measuring the same parts over multiple readings.

Gauge Linearity - A measure of gauge accuracy variation when evaluated over the expected operating range.

Gauge R and R - Repeatability and Reproducibility of any measurement process.

Gauge Repeatability - Variation when one person repeatedly measures the same unit with the same measuring equipment.

Gauge Reproducibility - Variation between means when two or more people measure the same unit with the same measuring equipment at the same time.

Gauge Stability - Variation obtained when the same person measures equipment over an extended period of time.

Gauge Study - The act of carrying out an experiment to establish the Repeatability and Reproducibility of a measurement system. (also known as Measurement System Analysis (MSA))

Green Belt - A process improvement project team leader who is trained and certified in Six Sigma methodology and tools and who is responsible for successful project execution. Six Sigma role similar in function to Black Belt, but length of training and project scope are reduced.

Heijunka - Production levelling by allocating production slots at regular intervals to different models.

Histogram - A vertical bar chart of a population distribution in terms of frequencies.

Homogeneity of Variance - The test used to establish whether the variances of two groups of the data are equal. Used as a prerequisite to a 2-sample hypothesis test for equal means.

Hoshin Kanri - Also called Policy Deployment – linking individual and departmental objectives to company objectives.

Hypothesis - When used as a statistical term, it is a theory proposed for comparing means and standard deviations of two or more data sets, or one data set against a target. A "null" hypothesis states that the data sets are from the same statistical population, while the "alternate" hypothesis states that the data sets are not from the same statistical population.

Independent Variable - A variable whose value is independent of the value of another variable.

In-process Supermarket - Small inventory holding areas used where one process is feeding many others. The process tops up the supermarket to standard inventory levels and only produces parts to replace those taken from the supermarket.

Instability - Unnaturally large fluctuations in a process input or output characteristic.

Interaction - The tendency of two or more variables to produce an effect in combination which neither variable would produce if acting alone.

Interval - Numeric categories with equal units of measure.

Jidoka - Separation of man from machine, allowing workers to control more than one piece of equipment.

JIT - Providing goods or services Just-in-Time to requirements

Kaizen - Japanese philosophy of ongoing improvement.

Kanban - Literally ‘signal’, used as the system between processes to facilitate Just-in-Time production and low inventories. Often a card or ticket is used as the signal. Modern technology allows for wireless signalling systems.

Key Process Input Variable (KPIV) - The vital few input variables, called "Xs" (normally 2-6), that drive 80% of the observed variations in the process output characteristic ("Y").

Key Process Output Variable (KPOV) - The Critical to Quality characteristics of a process as deemed by the customer.

Lean - The methodology used to remove waste from any process.

Lean Enterprise - An organisation where waste and cycle time are minimised through the Value Stream.

Lean Manufacturing - Term coined by Womack and Jones to describe the Toyota Production System in their book, ‘The Machine That Changed the World’.

Line Charts - Charts used to track performance.

Losses - Categories of stoppages used for analysis in Total Productive Maintenance (TPM), combines Availability, Performance and Quality of output.

Lower Control Limit (LCL) - A horizontal line plotted on a control chart which represents the lowest process deviation that should occur if the process is in control.

Master Black Belt - A person who is an "expert" on Six Sigma techniques and on project implementation. Master Black Belts play a major role in training, coaching and in removing barriers to project execution in addition to overall promotion of the Six Sigma philosophy.

Mean - Sum of all measurements divided by the total number of measurements. Statistic which is used to estimate the population mean.

Mean Time Between Failure (MTBF) - Average time to failure for a statistically significant population of a product operating in its normal environment.

Measurement System Analysis (MSA) - Means of evaluating a continuous or discrete measurement system to quantify the amount of variation contributed by the measurement system.

Median - The middle value in a group of measurements when ordered from low to high.

Milk Run - Picking up small shipments from multiple suppliers for delivery to manufacturing. Can be either internal or from external suppliers. Facilitates lean manufacturing as each load contains small quantities of many different parts.

Mistake-Proofing - Mistake-Proofing is a proactive technique used positively to prevent errors from occurring. (also known as Poka-Yoke)

Mixture Designs - A type of Response Surface Method Design of Experiment (RSM DoE) where the output of the process is dependent on the relative quantities (proportions) of several components and must always sum to a constant value

Muda - Waste. Any activity which does not transform material into customer requirements.

Multi-Vari - Method used in the measure/analyse phase of Six Sigma methodology to display in graphical terms variation within and between parts, machines, shifts, plants or processes.

Non Parametric Tests - A series of tests of medians for testing a data set against a target, two distributions against each other or more than two distributions against each other.

Nonconforming Unit - A unit which does not conform to one or more specifications, standards, and/or requirements.

Nonconformity - A condition within a unit which does not conform to a specification, standard, and/or requirement; often referred to as a defect; any given non-conforming unit can have the potential for more than one type of nonconformity.

Normal Distribution - A continuous, symmetrical density function characterised by a bell-shaped curve.

Null Hypothesis - An assertion to be proven by statistical analysis where two or more data sets are stated to be from the same population.

OEE (Overall Equipment Effectiveness) - A measure of equipment performance developed in Total Productive Maintenance. Combines Availability, Performance and Quality of output.

One Piece Flow - Linking processes one piece at a time through a number of operations.

OTIF - On Time in Full. A common measure of performance to agreed schedule.

Out of Control - Condition which applies to statistical process control chart where plot points fall outside of the control limits or fail an established run or trend criteria, all of which indicate that an assignable cause is present in the process.

P Charts - Charts used to plot percent defectives in a sample where sample size is variable.

Parameter - Quantities that define characteristics of a system or mathematical function.

Pareto Chart - A chart which places common occurrences in rank order.

PDCA - Plan, Do, Check, Act, sometimes called the Deming Wheel or Shewhart improvement cycle.

Plackett Burman - A type of Design of Experiments (DoE) that allows many inputs to be varied at the same time but is still able to expose the Main Effects. An input factor screening process. Often used to reduce the number of factors in a Full Factorial Experiment.

Pre-Control - Simplified Statistical Process Control procedure. Often used on a new process or existing one where no historic data exists. Can lead to additional work to control the process within customer specifications.

Planned Maintenance - Any preventive or corrective maintenance, which aims to eliminate problems through planned activity.

Poisson Distribution - A statistical distribution associated with attribute data (the number of non-conformities found in a unit) which can be used to predict first pass yield.

Poka-Yoke - Japanese term for Mistake-Proofing. Mistake-Proofing is a proactive technique used to positively prevent errors from occurring.

Policy Deployment - Also called Hoshin Kanri, linking individual and departmental objectives to company objectives.

Population - The entire set of items or data from which a sample is drawn.

Precision to Tolerance Ratio (P/T) - A ratio used to explain the amount of a specification range that is consumed by 99% confidence interval of the measurement system error.

Process Failure Mode Effects Analysis (PFMEA) - The technique identifies and documents potential failure modes and numerically identifies the risk of current process steps producing defects in terms of the severity, probability of occurrence and detectability.

Prevention - Predicting a future event and taking corrective action before that event occurs.

Preventive Maintenance - Any time or condition based activity which aims to prevent failures.

Probability - The chance of an event happening. Expressed as a percentage.

Problem - A deviation from a specified standard.

Process - A particular method of doing something, generally involving a number of steps or operations.

Process Average - The central tendency of a given process output over a defined time period.

Process Control Chart - A number of graphs upon which data are plotted against control limits that are calculated solely from the data itself.

Process Map - A detailed step by step pictorial sequence of a process often showing inputs and outputs.

Process Step - One part of a process map. Often the focus of an improvement project.

Process Variation - The range of values which a given process output displays.

Producer Risk - Probability of rejecting a lot when, in fact, the lot should have been accepted. (see alpha risk)

Quality Function Deployment (QFD) - A disciplined matrix methodology used for documenting and transforming customer requirements into measurable process outputs.

R Chart (Range Chart) - Plot of the difference between the highest and lowest in a subgroup. Normally associated with the range control portion of an X bar and R chart.

Random Cause - An inherent natural source of variation.

Random Sample - Selecting a sample such that each item in the population has an equal chance of being selected; lack of predictability; without pattern.

Random Variable - A variable which can assume any value from a distribution which represents a set of possible values.

Random Variations - Variations in data which result from causes which cannot be pinpointed or controlled.

Range - The difference between the highest and lowest values in a "subgroup" sample.

Rank - Values assigned to items in a sample to determine their relative occurrence in a population. The highest Rank item is the most frequently occurring item.

Rational Subgroup - A subgroup is usually made up of consecutive pieces chosen from the process stream. Any changes, shifts and drifts in the process will appear as differences between the subgroups, selected over time.

RCM (Reliability Centred Maintenance) - A procedure for ensuring zero failures of equipment and machinery.

Regression - A statistical technique for determining the best mathematical expression that describes the functional relationship between one response and one or more independent variables.

Replication - Repeat observations made under identical test conditions.

Representative Sample - A sample which accurately reflects a specific condition or set of conditions within the population.

Response Surface Methodology (RSM) - A graphical (pictorial) analysis technique used in conjunction with Design of Experiments for determining optimum process parameter settings.

Robust - The condition or state in which a response parameter exhibits a high degree of resistance to external causes of a non-random nature.

Rolled Throughput Yield (RTY) - The product (series multiplication) of all of the individual first pass yields of each step of the total process.

Risk Priority Number (RPN) - The product of the severity, occurrence and detection ratings from a Failure Modes and Effects Analysis. (FMEA)

Sample - One or more observations drawn from a larger collection of observations or population.

Scatter Diagrams (Graphs) - Charts which allow the study of correlation, i.e., the relationship between two variables or data sets.

SIPOC - A high-level process map. Stands for Supplier-Inputs-Process-Outputs-Customer.

Six Sigma - A term coined by Motorola to express process capability in parts per million. A Six Sigma process generates a maximum defect probability of 3.4 parts per million (PPM) when the amount of process shifts and drifts are controlled over the long term to less than +1.5 standard deviations. A methodology using a structured process and data analysis to reduce process defects.

Skewed Distribution - A non-symmetrical distribution having a tail in either a positive or negative direction.

SMED (Single Minute Exchange of Die) - A technique invented by Shigeo Shingo to help reduce set up time to the absolute minimum.

SOP (Standard Operating Procedure) - Documents the agreed standard way of performing a particular operation.

SPC (Statistical Process Control) - Control of processes usually based on measuring and recording data to detect process variation.

Special Cause - A process input variable that can be identified and that contributes in an observable manner to non-random shifts in process mean and/or standard deviation.

Sporadic Loss - Failure of equipment which has noticeable effects on production.

Stable Process - A process which is free of assignable causes, e.g. in statistical control.

Standard Deviation - A statistical index of variability which describes the process spread (range) or width of a distribution.

Subgroup - A logical grouping of objects or events which displays event-to-event variations.

Symptom - That which serves as evidence of something not fully understood in factual terms.

Taguchi methods - Statistical methods developed by Genichi Taguchi to improve the quality of manufactured goods. He was an innovator of Design of Experiments.

Takt Time - The rhythm of production, available time divided by the number of parts required. (E.g. How often is one required? 1 every 10 seconds)

Test of Significance - A statistical procedure used to determine whether or not a process observation differs from the Normal Expected Distribution by an amount greater than that due to random variation alone.

TPM (Total Productive Maintenance) - Equipment improvement approach encompassing several tools and techniques involving operators with everyday maintenance activities and maintenance with weekly/monthly tasks.

TQM (Total Quality Management) - Management development of Total Quality Control re-introduced to the West from Japan in the 1980’s.

TRIZ - Theory of Inventive Problem Solving. Innovation process which uses matrices to resolve apparent contradictions e.g. high quality, low cost.

Type 1 Error - The probability of accepting the alternate hypothesis when, in reality, the null hypothesis is true. (Alpha Risk)

Type 2 Error - The probability of accepting the null hypothesis when, in reality, the alternate hypothesis is true. (Beta Risk)

Upper Control Limit (UCL) - A horizontal line plotted on a control chart which represents the highest process deviation that should occur if the process is in control.

Value Adding Activities - Anything which the customer is willing to pay for in the transformation of material into customer requirements. The opposite of Waste.

Value Stream Mapping - A process mapping technique which charts both material and information flow exposing non value added steps. A current and future state map is normally developed, leading to a series of continuous improvement projects.

Variable - A characteristic that may take on different values.

Variable Data - Data collected from a process input or output where the measurement scale has a significant level of subdivisions or resolution., e.g. ohms, voltage, diameter.

Waste - Any activity which does not transform material into customer requirements. See Muda and 7 Wastes.

X - An independent input variable that may or may not have any relationship to a specified output.

X Bar and R Charts - Control of processes based on measuring and recording the average and the range of a process output for specified subgroup size data to detect process position and variation.

Y - A dependent output variable produced to meet customer requirements of cost, quality and time.

Yellow Belt - Yellow Belts are a vital part of any successful Six Sigma deployment. They work as team members on Black and Green Belt improvement projects. They spread project based process improvement and culture change throughout an organisation.

Yield - The percentage of the total process amount that is deemed to be "good".

Z Score - The name given to the Six Sigma benchmarking method. A process that is operating at a Z score of six will produce 3.4 parts per million defects in the long term.

Zero Quality Control (ZQC) - 100% inspection is achieved through mistake proofing which is inexpensive and requires little effort.

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