ASQ - Six Sigma Forum



Sample: In acceptance sampling, one or more units of product (or a quantity of material) drawn from a lot for purposes of inspection to reach a decision regarding acceptance of the lot.

Sample size: [n] The number of units in a sample.

Sample standard deviation chart (S chart): A control chart in which the subgroup standard deviation, s, is used to evaluate the stability of the variability within a process.

Sampling at random: As commonly used in acceptance sampling theory, the process of selecting sample units so all units under consideration have the same probability of being selected. Note: Actually, equal probabilities are not necessary for random sampling--what is necessary is that the probability of selection be ascertainable. However, the stated properties of published sampling tables are based on the assumption of random sampling with equal probabilities. An acceptable method of random selection with equal probabilities is the use of a table of random numbers in a standard manner.

Sampling, double: Sampling inspection in which the inspection of the first sample leads to a decision to accept a lot, reject it or take a second sample; the inspection of a second sample, when required, then leads to a decision to accept or to reject the lot.

Sampling, multiple: Sampling inspection in which, after each sample is inspected, the decision is made to accept a lot, reject it or to take another sample; but there is a prescribed maximum number of samples, after which a decision to accept or reject the lot must be reached. Note: Multiple sampling as defined here has sometimes been called "sequential n sampling" or "truncated sequential e sampling." The term "multiple sampling" is recommended by this standard.

Sampling, single: Sampling inspection in which the decision to accept or to reject a lot is based on the inspection of a single sample.

Sampling, unit: Sequential sampling inspection in which, after each unit is inspected, the decision is made to accept a lot, reject it or to inspect another unit.

Satisfier: A term used to describe the quality level received by a customer when a product or service meets expectations.

Scatter diagram: A graphical technique to analyze the relationship between two variables. Two sets of data are plotted on a graph, with the y-axis being used for the variable to be predicted and the x-axis being used for the variable to make the prediction. The graph will show possible relationships (although two variables might appear to be related, they might not be: those who know most about the variables must make that evaluation). The scatter diagram is one of the "seven tools of quality."

Scientific management/approach: A term referring to the intent to find and use the best way to perform tasks to improve quality, productivity and efficiency.

Scorecard: A scorecard is an evaluation device, usually in the form of a questionnaire, that specifies the criteria customers will use to rate your business's performance in satisfying their requirements.

Self-directed work team (SDWT): A type of team structure in which much of the decision making regarding how to handle the team's activities is controlled by the team members themselves.

Service level agreement: A formal agreement between an internal provider and an internal receiver (customer).

Seven tools of quality: Tools that help organizations understand their processes to improve them. The tools are the cause and effect diagram, check sheet, control chart, flowchart, histogram, Pareto chart and scatter diagram (see individual entries).

Shainin, Dorian (deceased): An Honorary Member of ASQ, Shainin developed a discipline called statistical engineering. He was in charge of quality control at a larger division of United Technologies Corp. and later did consulting for more than 900 organizations. Shainin also was on the faculty of the University of Chicago and wrote more than 100 articles and several books.

Shewhart cycle: See "plan-do-check-act cycle."

Shewhart, Walter A. (deceased): Referred to as the father of statistical quality control because he brought together the disciplines of statistics, engineering and economics. He described the basic principles of this new discipline in his book Economic Control of Quality of Manufactured Product. Shewhart, ASQ's first Honorary Member, was best known for creating the control chart. Shewhart worked for Western Electric and AT&T Bell Telephone Laboratories, in addition to lecturing and consulting on quality control.

Sigma: A term taken from the Greek letter σ (sigma), used in statistics as a measure of variation. The sigma value for a business process refers to the standard deviation and indicates how well that process is performing.

Sigma Levels

Sigma level

Defects per million opportunities (DPMO)













Signal to noise ratio (S/N ratio): A mathematical equation that indicates the magnitude of an experimental effect above the effect of experimental error due to chance fluctuations.

Single minute exchange of dies (SMED): SMED refers to the theory and techniques for performing setup operations in under ten minutes, the number of minutes expressed in a single digit.

SIPOC diagram: Related to the process map, a SIPOC diagram is a tool for defining business processes by listing suppliers, inputs, process, outputs, and customers. Requirements of the customers may also be included.

Six Sigma: A methodology that provides businesses with the tools to improve the capability of their business processes. This increase in performance and decrease in process variation lead to defect reduction and improvement in profits, employee morale and quality of product.

Six Sigma culture: An organization-wide culture that focuses on metrics and measurement, customer requirements, openness about defects, and empowerment and teamwork as it strives for continuous improvement by using the Six Sigma methodology.

Six Sigma "belts": System for designating experience levels of Six Sigma practitioners. Based on the perceived similarities of martial artists and Six Sigma experts, who attack problems through rigorous application of statistical techniques and the selective use of basic quality tools. See also "Green Belt," "Black Belt," and "Master Black Belt."

Six Sigma quality: A term generally used to indicate a process is well controlled, (±6 sigma from the centerline in a control chart). The term is usually associated with Motorola, which named one of its key operational initiatives "Six Sigma quality."

Skew: The shape of a curve of an asymmetric distribution. Forms include positive skewness for skew right and negative skewness for skew left. (Quality Council of Indiana)

Skew left: Negative skewness has greater scatter and a longer tail to the left. (Quality Council of Indiana)

Skew right: Positive skewness has greater scatter and a longer tail to the right of the mean. (Quality Council of Indiana)

Soft data: Data that cannot be measured or specifically quantified, such as survey data that ask respondents to provide their "opinion" about something.

Software quality assurance (SQA): A planned and systematic approach to the evaluation of the quality of and adherence to software product standards, processes and procedures. SQA includes the process of assuring that standards and procedures are established and are followed throughout the software acquisition life cycle.

SPC & control charts: The application of statistical methods to analyze data, study and monitor process capability and performance. (Steve Littleton)

Special causes: Causes of variation that arise because of special circumstances. They are not an inherent part of a process. Special causes are also referred to as assignable causes (see also "common causes").

Specification: A document that states the requirements to which a given product or service must conform.

Spread (range): A smaller is better measure of variability and dispersion equal to the absolute difference between the largest observed value and the smallest observed value in a given sample. Given by: R=L-S where R is the range of the sample, L is the largest value in the sample, and S is the smallest value in the sample. (Quality Council of Indiana).

Sponsor: The person who supports a team's plans, activities and outcomes; the team's "backer."

Stable operations: Processes from which special-cause variation has been removed and common-cause variation has been sufficiently reduced to make outputs consistent and predictable.

Stages of team growth: Four stages that teams move through as they develop maturity over time: forming, storming, norming and performing.

Stakeholder: Any individual, group or organization that will have a significant impact on or will be significantly impacted by the quality of the product or service an organization provides.

Standard: The metric, specification, gage, statement, category, segment, grouping, behavior, event or physical product sample against which the outputs of a process are compared and declared acceptable or unacceptable.

Standard deviation (statistical): A computed measure of variability indicating the spread of the data set around the mean.

Standard work: A precise description of each work activity specifying cycle time, takt time (see listing), the work sequence of specific tasks and the minimum inventory of parts on hand needed to conduct the activity.

Statistical process control (SPC): The application of statistical techniques to control a process. The term "statistical quality control" is often used interchangeably with "statistical process control."

Statistical quality control (SQC): The application of statistical techniques to control quality. The term "statistical process control" is often used interchangeably with "statistical quality control," although statistical quality control includes acceptance sampling as well as statistical process control.

Statistics: A field that involves the tabulating, depicting and describing of data sets; a formalized body of techniques characteristically involving attempts to infer the properties of a large collection of data from inspection of a sample of the collection.

Strategic planning: The process by which an organization envisions its future and develops strategies, goals, objectives and action plans to achieve that future.

Stretch goals: A set of goals designed to position the organization to meet future requirements.

Structural variation: Variation caused by regular, systematic changes in output, such as seasonal patterns and long-term trends.

Supplier: A source of materials, service or information input provided to a process.

Supplier quality assurance: Confidence a supplier's product or service will fulfill its customers' needs. This confidence is achieved by creating a relationship between the customer and supplier that ensures the product will be fit for use with minimal corrective action and inspection. According to J. M. Juran, there are nine primary activities needed: 1. define product and program quality requirements, 2. evaluate alternative suppliers, 3. select suppliers, 4. conduct joint quality planning, 5. cooperate with the supplier during the execution of the contract, 6. obtain proof of conformance to requirements, 7. certify qualified suppliers, 8. conduct quality improvement programs as required and 9. create and use supplier quality ratings.

Supply chain: The series of suppliers relating to a given process.

Surveillance: The continual monitoring of a process; a type of periodic assessment or audit conducted to determine whether a process continues to perform to a predetermined standard.

Survey: The act of examining a process or of questioning a selected sample of individuals to obtain data about a process, product or service.

Symptom: An observable phenomenon arising from and accompanying a defect.

System: A group of interdependent processes and people that together perform a common mission.

System kaizen: Improvement aimed at an entire value stream.

Systematic measurement error. (d) (or bias error): Average deviation of the measurement result from the true value by which the measurement result increases, when repeating the measurement a large number of times.

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