glossary of quality terms

7/31/2019 Glossary of Quality Terms

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Glossary

benchmarking A technique that involves comparing one's own processes to excellent examples of similar processes in other organizations or departments. Through benchmarking, rapid learning canoccur, and processes can undergo dramatic improvements.

brainstorming A tool used to encourage creative thinking and new ideas. A group formulates andrecords as many ideas as possible concerning a certain subject, regardless of the content of the ideas.No discussion, evaluation, or criticism of ideas is allowed until the brainstorming session is complete.

calibration Comparison of a measurement instrument or system of unverified accuracy to ameasurement instrument or system of known accuracy to detect any variation from the requiredperformance specification.

certificate of compliance A document signed by an authorized party affirming that the supplier of aproduct or service has been tested/analysed/measured/verified to meet the requirements of relevantspecifications. See also 'Certificate of Analysis'.

Certificate of Conformance (Certificate of Conformity) A document signed by an authorized partyaffirming that a product or service has met the requirements of the relevant specifications, contract, orregulation.

certification audits Audits relating to registration (e.g., ISO 9001 audits).

common cause A source of variation that is always present as part of the random variation inherent inthe process itself. Its origin can usually be traced to an element of the system which only managementcan correct.

competence Demonstrated ability to apply knowledge skills.

continuous improvement / CI On-going improvement of any and all aspects of an organization includingproducts, services, communications, environment, functions, individual processes, etc. ContinuousImprovement Action taken to find ways in improve processes, decrease variation , decrease costs, andimprove effectiveness of the organization.

contract review Contract review involves the steps associated with contracting with suppliers. Thesesteps involve acceptance of the contract or order, the tender of a contract, and review of the contract.

contrition Forgiveness for error or mistake.

control Three commonly-used versions of this word: (supervision)- to influence or manipulate anemployee's behavior through the threat of consequences or the promise of reward, whether theseare explicit or implied; (engineering)- to influence or manipulate a process through feedback orfeedforward; (statistical)- a description of behavior of the variation in the output of a process.

control chart A chart that indicates upper and lower statistical control limits, and an average line, forsamples or subgroups of a given process. If all points on the control chart are within the limits, variation
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may be ascribed to common causes and the process is deemed to be "in control." If points fall outsidethe limits, it is an indication that special causes of variation are occurring, and the process is said tobe "out of control."

control limit A statistically-determined line on a control chart used to analyze variation within a process.

If variation exceeds the control limits, then the process is being affected by special causes and is said tobe "out of control." A control limit is not the same as a specification limit.

cost of poor quality The costs incurred by producing products or services of poor quality. These costsusually include the cost of inspection, rework, duplicate work, scrapping rejects, replacements andrefunds, complaints, and loss of customers and reputation.

count chart (c chart )An attributes data control chart that evaluates process stability by charting thecounts of occurrences of a given event in successive samples.

count-per-unit chart (u chart ) A control chart that evaluates process stability by charting the number of

occurrences of a given event per unit sampled, in a series of samples.

cp/ CP Commonly used process capability index defined as [USL (upper spec limit) - LSL(lower spec limit)]/ [6 x sigma], where sigma is the estimated process standard deviation.

cpk / CPK Commonly used process capability index defined as the lesser of USL - m / 3sigma or m - LSL /3sigma, where sigma is the estimated process standard deviation.

Philip Crosby One of the quality guru's. Crosby founded several consulting agencies including CareerIV, Philip Crosby Associates, and the Quality College. He has authored several books including Quality IsFree and Quality Without Tears. Crosby is well-known for his theory of "zero defects."

cumulative sum chart Control chart that shows the cumulative sum of deviations from a set value insuccessive samples. Each plotted point indicates the algebraic sum of the last point and all deviationssince. PathMaker does not support cumulative sum charts.

customer Any recipient of a product or service; anyone who is affected by what one produces. Acustomer can be external or outside the organization, or they can be internal to the organization.

decision matrix A tool used to evaluate problems, solutions, or ideas. The possibilities are listed downthe left-hand side of the matrix and relevant criteria are listed across the top. Each possibility is thenrated on a numeric scale of importance or effectiveness (e.g. on a scale of 1 to 10) for each criterion,

and each rating is recorded in the appropriate box. When all ratings are complete, the scores for eachpossibility are added to determine which has the highest overall rating and thus deserves the greatestattention.

defect An error in construction of a product or service that renders it unusable; an error that causes aproduct or service to not meet requirements.

Deming cycle Alternate name for the Plan-Do-Check-Act cycle, a four-stage approach to problem-
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solving. It is also sometimes called the Shewhart cycle.

Deming, W. Edwards Known as the father of quality control. Deming began his work in quality controlin the United States during World War II to aid the war effort. After the war, he went to Japan to helpin the rebuilding of their country. His methods of quality control became an integral part of Japanese

industry. Deming is a celebrated author and is well-known for his "14 Points" for effective management.

diagnostic journey (remedial journey) A problem-solving approach in which a problem is investigated bylooking first at symptoms, and gradually working back towards root causes. Once root causes have beenestablished, experimentation and tracking are used in the remedial journey - the finding of a cure for theroots of the problem.

DOE (design of experiments ) The science of designing sets of experiments which will generate enoughuseful data to make sound decisions without costing too much or taking too long.

employee involvement Regular participation of employees in decision-making and suggestions. The

driving forces behind increasing the involvement of employees are the conviction that more brains arebetter, that people in the process know it best, and that involved employees will be more motivated todo what is best for the organization.

empowerment Usually refers to giving employees decision-making and problem-solving authority withintheir jobs.

external customer A person or organization outside your organization who receives the output of aprocess. Of all external customers, the end-user should be the most important.

Failure Mode Effects Analysis (FMEA) A technique that systematically analyzes the types of failures

which will be expected as a product is used, and what the effects of each "failure mode" will be.

facilitator Person who helps a team with issues of teamwork, communication, and problem-solving.A facilitator should not contribute to the actual content of the team's project, focusing instead as anobserver of the team's functioning as a group.

fishbone diagram Another name for an Ishikawa diagram or cause & effect diagram, derived from theshape of the diagram as used by its creator, Kaoru Ishikawa.

flowchart A graphical representation of a given process delineating each step. A flowchart is used todiagram how a process actually functions and where waste, error, and frustration enter the process.

force field analysis A tool, developed by social psychologist Kurt Lewin, which is used to analyze theopposing forces involved in causing/resisting any change. It is shown in balance sheet format with forcesthat will help (driving forces) listed on the left and forces that hinder (restraining forces) listed on theright.

frequency distribution An organization of data, usually in a chart, which depicts how often differentevents occur. A histogram is one common type of frequency distribution, and a frequency polygon is
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another.

Gantt chart A bar chart that shows planned work and finished work in relation to time. Each task in a listhas a bar corresponding to it. The length of the bar is used to indicate the expected or actual duration of the task.

histogram A specialized bar chart showing the distribution of measurement data. It will pictorially revealthe amount and type of variation within a process.

Hoshin Kanri : Japanese term for hoshin planning, a form of interactive strategic planning which aids theflow of information up and down the organizational layers in a systematic, productive way.

Hoshin planning A method of strategic planning for quality. It helps executives integrate qualityimprovement into the organization's long-range plan. According to the GOAL/QPC Health CareApplication Research Committee, "Hoshin Planning is a method used to ensure that the mission, vision,goals, and annual objectives of an organization are communicated to and implemented by everyone,

from the executive level to the 'front line' level."

indicator Quantitative measure of performance. Indicators are usually ratios comparing the number of occurrences a certain phenomenon and the number of times the phenomenon could have occurred.

internal customer Someone within your organization, further downstream in a process, who receivesthe output of your work.

Ishikawa diagram Another name for the cause & effect diagram, after its inventor, Kaoru Ishikawa .

Joseph M. Juran One of the great quality gurus, and, like Deming, an early student of the work of WalterShewhart at Western Electric. His work has specialized in linking management to quality engineering.Dr. Juran is the founder of the Juran Institute which has long been the vehicle of his work in qualitymanagement and is well-known for espousing "the quality trilogy" of quality planning, quality control,and quality improvement. Juran has authored many books and other works in an effort to spreadawareness of quality management ideas and applications.

just-in-time instruction Training given as needed for immediate application, without lag time and theusual loss of retention.

just-in-time / JIT A concept that manufacturing or procuring product "just in time" for delivery isefficient.

Kaizen / kaizen A Japanese word meaning continuous improvement through constant striving to reachhigher standards.

Kaoru Ishikawa One of Japan's quality control pioneers. He developed the cause & effect diagram(Ishikawa diagram) in 1943 and published many books addressing quality control. In addition to his workat Kawasaki, Ishikawa was a long-standing member of the Union of Japanese Scientists and Engineersand an assistant professor at the University of Tokyo.
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KJ method Another name for the affinity diagram, after its inventor, Kawakita Jiro .

mean The average of a group of measurement values. Mean is determined by dividing the sum of thevalues by the number of values in the group.

median The middle of a group of measurement values when arranged in numerical order. For example,in the group (32, 45, 78, 79, 101), 78 is the median. If the group contains an even number of values, themedian is the average of the two middle values.

metacraftsmanship A reference to the ideas shared by quality improvement, reengineering,management, leadership, and customer-driven production. Although these theories have much incommon, they are often treated as separate and disparate approaches to improving a business.Metacraftsmanship focuses on overcoming the losses to society which are engendered by specialization,and suggests ways of getting complex organizations to work the way a single craftsman would.

mission statement A written declaration of the purpose of an organization or project team.

Organizational mission or vision statements often include an organizational vision for the future, goals,and values.

mode The most frequently occurring value in a group of measurements. The most common valueobtained in a set of observations. For example, for a data set (3, 7, 3, 9, 9, 3, 5, 1, 8, 5), the unique modeis 3. Similarly, for a data set (2, 4, 9, 6, 4, 6, 6, 2, 8, 2), there are two modes: 2 and 6.

TODO A distribution with a single mode is said to be unimodal . A distribution with more than one modeis said to be bimodal , trimodal , etc., or in general, multimodal .

noise In the context of quality management, noise is essentially variability. For example, if you are

making ketchup, noise in the process comes from variations in the quality of incoming tomatoes, inchanges in ambient temperature and humidity, in variations in machinery performance, in variations inthe quality of human factors, etc.

nominal group technique Technique used to encourage creative thinking and new ideas, but ismore controlled than brainstorming. Each member of a group writes down his or her ideas and thencontributes one to the group pool. All contributed ideas are then discussed and prioritized.

np chart A control chart indicating the number of defective units in a given sample.

paradigm A way of thinking about a given subject that defines how one views events, relationships,

ideas, etc. within the boundaries of that subject.

Pareto chart A bar chart that orders data from the most frequent to the least frequent, allowing theanalyst to determine the most important factor in a given situation or process.

Pareto principle The idea that a few root problems are responsible for the large majority of consequences. The Pareto principle is derived from the work of Vilfredo Pareto , a turn-of-the-centuryItalian economist who studied the distributions of wealth in different countries. He concluded that
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a fairly consistent minority about 20% of people controlled the large majority about 80% of asociety's wealth. This same distribution has been observed in other areas and has been termed thePareto principle. It is defined by J.M. Juran as the idea that 80% of all effects are produced by only 20%of the possible causes.

percent chart / p chart

A control chart that determines the stability of a process by finding what percentage of total units in asample are defective.

pie chart A chart that compares groups of data to the whole data set by showing each group as a "slice"of the entire "pie." Pie charts are particularly useful for investigating what percentage each grouprepresents.

plan-do-check-act cycle / PDCA A four-step improvement process originally conceived of by WalterA. Shewhart . The first step involves planning for the necessary improvement; the second step is the

implementation of the plan; the third step is to check the results of the plan; the last step is to act uponthe results of the plan. It is also known as the Shewhart cycle, the Deming cycle, and the PDCA cycle.

policy deployment Another name for hoshin planning.

population Total set of items from which a sample set is taken.

process capability 1. A statistical measure indicating the inherent variation for a given event in a stableprocess, usually defined as the process width divided by 6 sigma.

process capability 2. Competence of the process, based on tested performance, to achieve certainresults.

Process Capability Index / PCI Measurement indicating the ability of a process to produce specifiedresults. Cp and Cpk are two process capability indices.

quality assurance / QA Traditionally refers to the systematic post-production checks, inspection, orreviews done to ensure quality of a product or service though in the strict sense of the definitionthat is an end of process quality control activity. Modern quality management systems considerQuality Assurance that through tools such Quality Audits , Quality Control , and specificallySystems Audits assures that the processes, tools, and safeguards are in place to produce qualityproducts

quality audit An independent investigation and assessment of quality activities and results to determinewhether or not the quality plan is effective and appropriate.

quality circle Quality improvement teams or groups, such as groups of employees formed for the studyof and sharing information regarding quality control issues and theory.

quality control / QC The use of techniques and activities that compare actual quality performance with
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goals and define appropriate action in response to a shortfall.

quality improvement / QIA systematic approach to the processes of work that looks to remove waste,loss, rework, frustration, etc. in order to make the processes of work more effective, efficient, andappropriate.

quality improvement team A group of employees that take on a project to improve a given process ordesign a new process within an organization.

quality function deployment / QFD A technique used to translate customer requirements intoappropriate goals for each stage of product or service development and output. The two approaches toquality function deployment are known as the House of Quality and the Matrix of Matrices.

quality loss function An algebraic function that illustrates the loss of quality that occurs when acharacteristic deviates from its target value. It is expressed often in monetary terms. Dr. Genichi Taguchicoined this term; his work suggests that quality losses vary as the square of the deviation from target.

range chart Control chart in which the range of the subgroup is used to track the instantaneousvariation within a process, i.e. the variation in the process at any one time, when many input factorswould not have time to vary enough to make a detectable difference. Range charts are usually pairedwith average charts for complete analysis.

recorder The team member that takes minutes during team meetings to capture team's progress. Oncethe team is well underway, this role can be rotated through out the group.

regression analysis A statistical technique used to determine the best mathematical expression todescribe the relationship between a response and independent variables.

reliability The probability of a product or service successfully doing its job under given conditions.

robustness The ability of a product or service to function appropriately regardless of external conditionsand other uncontrollable factors.

robust design An approach to the planning of new products and services that harnesses Taguchimethods.

run chart Also known as a line chart, or line graph. A chart that plots data over time, allowing you toidentify trends and anomalies.

sample A subset of a population used to represent the population in statistical analysis. Samples arealmost always random, which means that all individuals in the population are equally likely to be chosenfor the sample.

sample standard deviation chart (s-chart ) Control chart in which the standard deviation of the subgroupis tracked to determine the variation within a process over time. Sample standard deviation charts areusually paired with average charts for complete analysis.
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scatterplot A tool that studies the possible relationship between two variables expressed on the x-axisand y-axis of a graph. The direction and density of the points plotted will indicate various relationshipsor a lack of any relationship between the variables.

Seven Tools of Quality Quality improvement tools that include the histogram , Pareto chart , check

sheet , control chart , cause-and-effect diagram , flowchart , and scatter diagram .

Shewhart cycle Another name for the Plan-Do-Check-Act cycle. It is also sometimes called the Demingcycle.

Walter A. Shewhart The father of statistical process control or statistical quality control. He pioneeredstatistical quality control and improvement methods when he worked for Western Electric and BellTelephone in the early decades of the 20th century.

special cause Causes of variation in a process that are not inherent in the process itself but originatefrom circumstances that are out of the ordinary. Special causes are indicated by points that fall outside

the limits of a control chart.

specification limit An engineering or design requirement that must be met in order to produce asatisfactory product.

statistical process control (SPC) Analysis and control of a process through the use of statisticaltechniques, particularly control charts.

statistical quality control (SQC) Analysis and control of quality through the use of statistical techniques,essentially the same as SPC.

structural variation Variation caused by recurring system-wide changes such as seasonal changes orlong-term trends.

supplier Anyone whose output (materials, information, service, etc.) becomes an input to anotherperson or group in a process of work. A supplier can be external or internal to the organization.

Taguchi, Genichi Developed a set of practices known as Taguchi Methods, as they are known in theU.S., for improving quality while reducing costs. Taguchi Methods focus on the design of efficientexperiments, and the increasing of signal to noise ratios. Dr. Taguchi also articulated the developed thequality loss function. Currently, he is executive director of the American Supplier Institute and directorof the Japan Industrial Technology Institute.

tampering Dr. Deming cautions against tampering with systems that are "in control." It is very commonfor management to react to variation which is in fact normal, thereby starting wild goose chases aftersources of problems which don't exist. Tampering with stable processes actually increases variation.

tree diagram A chart used to break any task, goal, or category into increasingly detailed levels of information. Family trees are the classic example of a tree diagram. In PathMaker, the structure of thetree diagram is identical to that of the cause & effect diagram.
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timekeeper Team member who keeps track of time spent on each agenda item during team meetings.This job can easily be rotated among team members.

total quality management Managing for quality in all aspects of an organization focusing on employeeparticipation and customer satisfaction. Often used as a catch-all phrase for implementing various

quality control and improvement tools.

type I error Rejecting something that is acceptable. Also known as an alpha error.

type II error Accepting something that should have been rejected. Also known as beta error.

u chart A control chart showing the count of defects per unit in a series of random samples.

value-added Each time work is done to inputs to transform them into something of greater usefulnessas an end product.

variables data Data that is measured on a continuous and infinite scale such as temperature, distance,

and pressure rather than in discreet units or yes/no options. Variables data is used to create histograms,some control charts, and sometimes run charts.

variance A measure of deviation from the mean in a sample or population.

variation Change in the output or result of a process. Variation can be caused by common causes,special causes, tampering, or structural variation.

vision Often incorporated into an organizational mission (or vision) statement to clarify what theorganization hopes to be doing at some point in the future. The vision should act as a guide in choosingcourses of action for the organization.

zero defects Philip Crosby's recommended performance standard that leaves no doubt regarding thegoal of total quality. Crosby's theory holds that people can continually move closer to this goal bycommitting themselves to their work and the improvement process.

Coefficient of variation, CV. The relative standard deviation, i.e., the standard deviationexpressed as a percentage of the mean [CV=100(s/x)] .

Comparison graph, comparison plot . Used here to refer to the display of paired test results inwhich the test method values are plotted on the y-axis versus the comparison method values onthe xaxis.

Confidence interval, confidence range . The interval or range of values which will contain thepopulation parameter with a specified probability.

Control chart. "A graphical method for evaluating whether a process is or is not in a 'state of statistical control.' The determinations are made through comparison of the values of somestatistical measure(s) for an ordered series of samples, or subgroups, with control limits"
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[ASQ]. In healthcare laboratories, the Levey-Jennings chart is commonly used to plot the resultobserved for a stable control material versus time, usually the day or run number.

Control limits. "Limits on a control chart which are used as criteria for signalling the need foraction, or for judging whether a set of data does or does not indicate a 'state of control'" [ASQ].

Used here to refer to the defined limits or ranges of results expected due to the random error of the method, and beyond which some course of action should be taken. It is common in clinicallaboratories to use Levey-Jennings control charts with limits set as either the mean plus orminus 2 standard deviations, or the mean plus or minus 3 standard deviations.

Correlation coefficient, r. A statistic that estimates the degree of association between twovariables, such as the measurement result by a test method and the measurement result by acomparison method.

Criteria for acceptability. CLIA's term for the decision criteria applied to assess the validity of an analytical run. Another name for QC procedure, with emphasis on definition of the decisioncriteria or control rules for interpreting control measurements.

Dispersion . Refers to the spread of values observed for a variable. The standard deviation isa measure of dispersion, in contrast to the mean which is a measure of central tendency orlocation.

Histogram . A graph of a frequency distribution in which the rectangles on the horizontal or x-axis are given widths proportional to the intervals of the quantities being displayed, and heightsproportional to the frequency of occurrence of quantities within that interval. [CLSI]

Inaccuracy. "Numerical difference between the mean of a set of replicate measurements andthe true value. This difference (positive or negative) may be expressed in the units in which thequantity is measured, or as a percentage of the true value"

Mean. The arithmetic average of a set of values. A measure of central tendency of thedistribution of a set of replicate results. Often abbreviated by an x with a bar over it.

Measurand . Quantity intended to be measured. [ISO]

Method selection . The process of defining the laboratory requirements and choosing ananalytical method which has the desired characteristics. Application and methodologycharacteristics must be carefully considered when selecting the method.

Method validation. The process of testing a measurement procedure to assess its performanceand to validate that performance is acceptable. The magnitudes of the analytical errors areexperimentally determined and their acceptability for the application of the method is judgedversus defined requirements for quality in the form of maximum allowable errors.

Model. A mathematical equation that describes the behavior of a process as a function of its


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important characteristics.

Performance specification . A value or range of values for a performance characteristic,established or verified by the laboratory, that is used to describe the quality of patient testresults. [CLSI]

Preventive maintenance. The renewing or refurbishing or critical parts of a method on a regularbasis to prevent malfunctions.

Primary standard material. "Substance of known chemical composition and sufficient purity tobe used in preparing a primary standard solution"

Probability, p. The likelihood an event will occur, usually stated as a decimal fraction between 0and 1, 0 meaning that the event will never occur and 1 meaning that the event will always occur.For example, p=0.05 means there is a 5% chance that an event will occur. Commonly used inquality control to describe the chance that a run will be rejected.

Probability for error detection, P ed . A performance characteristic of a QC procedure thatdescribes how often an analytical run will be rejected when results contain errors in addition tothe inherent imprecision of the measurement procedure. Ideally, P ed should be 1.00 for errorsthat are medically significant. In practice, we generally aim for a P ed of 0.90 when selecting anddesigning QC procedures.

Probability for false rejection, P fr. A performance characteristic of a QC procedure thatdescribes how often an analytical run will be rejected when there are no errors occurring,except for the inherent imprecision of the measurement procedure. Ideally, P fr should be 0.00.In practice, we generally aim for a P fr of 0.05 or less.

Process capability. An industrial term used to describe how the inherent variability of aproduction process under stable operation compared to the allowable variation. SEcrit is anindex of process capability for an analytical testing process.

Process stability. Used here to characterize the performance of the measurement procedure interms of the frequency of analytic runs having medically important errors (f) that invalidate themedical usefulness.

Proficiency sample . A specimen containing analytes of unknown concentration or identificationthat is sent to laboratories participating in testing programs in order to independently verify thelaboratory technical competency. [CLSI]

Proficiency testing, PT. A program in which multiple specimens are periodically sent tomembers of a group of laboratories for analysis and/or identification; in which each laboratorysresults are compared with those of other laboratories in the group and/or with an assignedvalue, and reported to the participating laboratory and others.


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Proficiency testing criteria for acceptable performance, PT criteria. Defined limits about atarget value (TV) that are used to classify analytical performance as acceptable or not.

Provider performed microscopy, PPM. A special subset of moderately complex tests that maybe performed by physicians, dentists, nurse practioners and midwives, and physician assistants

as part of a patient examination.

QC, Quality control . A generic term that refers to the monitoring and assessment of laboratorytesting processes to identify problems and maintain performance.

QC acceptability criteria. The term used by CLIA to indicate the decision criteria or control rulesused to monitor test performance during a run of patient specimens.

QC planning process, QC Design, quality planning process. The steps to be followed to selectcontrol rules, N, and a Total QC strategy that are appropriate for the quality needed and theimprecision and inaccuracy observed for a laboratory test.

imprecision and inaccuracy observed for a laboratory test.

Quality . The totality of characteristics of an entity that bear on its ability to satisfy stated andimplied needs. [CLSI]

Quality assessment . CLIAs term for the overall system for assuring the quality of laboratory testresults. Includes the monitoring and assessment of general laboratory systems, as well as pre-analytic, analytic, and post-analytic systems, with the objective of identifying problems, makingcorrections, and improving the quality of testing services.

Quality assurance . Planned and systematic activities to provide adequate confidence thatrequirements for quality will be met. [CLSI, ISO]

Quality management . All activities of the overall management function that determine qualitypolicy objectives and responsibilities; and implement them by means such as quality planning,quality processes, quality control, quality assessment, and quality improvement within thequality system. [CLSI, ISO]

Quality planning model. Term used to describe an equation that shows the additive effectsof different factors that influence the variation of a test result. The analytical model relatesthe imprecision and inaccuracy of the measurement procedure and the sensitivity of the

control procedure to the total analytical error that is allowable. The clinical model includesthe analytical components plus pre-analytical components, such as within-subject biologicalvariation, etc., and relates them to the clinical decision interval or gray zone for interpreting atest result.

Quality system . The organizational structure, resources, processes, and procedures needed toimplement quality management. [CLSI, ISO]


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Random error, RE. An error that can be either positive or negative, the direction and exactmagnitude of which cannot be exactly predicted. In contrast, systematic errors are always in onedirection.

Reference values . All of the values observed for a particular determination when sampling a

population of individuals in defined states of health.

Sample. "The appropriate representative part of a specimen which is used in the analysis."[IFCC]

Six Sigma . A concept for world-class quality and a goal for process performance that requires6 SDs of process variation to fit within the tolerance limit or quality requirement of a process.Applied in the Method Decision Chart as a criterion that requires bias + 6 SDs to be less than TE a,the allowable total error for the test.

Standard. "Material or solution with which the sample is compared in order to determine the

concentration or other quantity. The compound term calibration standard should be usedwhenever needed to avoid confusion with other technical or colloquial meanings of the wordstandard." [IFCC]

Standard deviation, s. A statistic that describes the dispersion or spread of a set of measurements about the mean value of a gaussian or normal distribution. Calculated from theequation:

where n is the number of measurements, and xi is an individual measurement

Statistical quality control. Those aspects of quality control in which statistics are applied, incontrast to the broader scope of quality control which includes many other procedures, suchas preventive maintenance, instrument function checks, and performance validation tests.Statistical QC procedures are often used to monitor routine performance of a method and toalert the laboratory when the performance of a method changes.

Statistical control limits. As used with Levey-Jennings and Westgard multirule types of QCprocedures, these are the lines drawn on control charts to define the range of results expecteddue to the random error of the method. The limits are often obtained from a group of 20 ormore measurements on a particular control material by calculating the mean and standard

deviation, then using multiples such as the mean plus/minus 3s, 2s, or 1s to establish rejectionlimits for different control rules.

Statistical process control. A general term used to describe those aspects of a control system inwhich statistics are applied to determine whether observed measurements fall within the rangeexpected due to the random variation of the process. Industrial process control proceduresprovided the basis for introduction of statistical control in healthcare laboratories, however,


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industrial process control procedures often use the mean and range of a group of controlmeasurements .

Traceability . A property of the result of a measurement or the value of a standard wherebyit can be related to stated references, usually national or international standards, through an

unbroken chain of comparison, all having stated uncertainties. [CLSI]

Validation . Action or process of proving that a procedure, process, system, equipment, ormethod used works as expected and achieves the intended results. [CLSI]

Variable. A quantity of interest, whose value or magnitude fluctuates or changes.

Variance. The standard deviation squared. If there are independent sources of errors, thevariance of the total error is the sum of the variances due to the individual sources of error.

Verification . The confirmation by examination and provision of objective evidence that specifiedrequirements have been fulfilled. [CLSI]

glossary of quality terms

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