There are a lot of terms that are specific to Lean and Six Sigma. If you are unsure about the meaning of a term, please feel free to check our Lean and Six Sigma Glossary for a definition. If you do not find the term you are looking for, please contact us. We would be happy to answer your questions, and we may add your term to the glossary in the future.

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Using a smaller group to represent the whole; foundation of statistics which can save time, money, and effort; allows for more meaningful data; can improve accuracy of measurement system.

Sampling bias

When data can be prejudiced in one way or another and do not represent the whole.

Scatter plot or diagram

Graph used to show relationship-or correlation-between two factors or variables. See also Correlation Coefficient.


Defines the boundaries of the process or the Process Improvement project; clarifies specifically where opportunities for improvement reside (start- and end-points); defines where and what to measure and analyze; needs to be within the sphere of influence and control of the team working on the project-the broader the scope, the more complex and time-consuming the Process Improvement efforts will be.

Should-be process mapping

Process-mapping approach showing the design of a process the way it should be (e.g., without non-value-adding activities; with streamlined workflow and new solutions incorporated). Thus contrasts with the “As-Is” form of process mapping. See also Process Redesign, Value- Adding Activities; Non-Value-Adding Activities.


Acronym for Suppliers, Inputs, Process, Outputs, and Customer; enables an “at-a-glance,” high-level view of a process.

Six Sigma or 6 Sigma

1. Level of process performance equivalent to producing only 3.4defects for every one million opportunities or operations.

2. Term used to describe Process Improvement initiatives using sigma-based process measures and/or striving for Six Sigma-level performance.

Solution statement

A clear description of the proposed solution(s); used to evaluate and select the best solution to implement.


Statistical Process Control is use of data gathering and analysis to monitor processes, identify performance issues, and determine variability/ capability. See also Run Charts; Control Charts.

Special cause

Instance or event that impacts processes only under “special” circumstances -i.e., not part of the normal, daily operation of the process. See Common Cause; Variation.

Sponsor (or Champion)

Person who represents team issues to senior management; gives final approval on team recommendations and supports those efforts with the Quality Council; facilitates obtaining of team resources as needed; helps Black Belt and team overcome obstacles; acts as a mentor for the Black Belt


A pictorial display of all the components in the DMAIC process, used by the team to arrive at a solution; used in presentations to Sponsor, senior management, and others.


Looking at data in multiple layers of information such as what (types, complaints, etc.), when (month, day, year, etc.), where (region, city, state, etc.), and who (department, individual).

Stratified sampling

Dividing the larger population into subgroups, then taking your sample from each subgroup.


Any person or organization that feeds inputs (products, services, or information) into the process; in a service organization, many times the customer is also the supplier.

Systematic sampling

Sampling method in which elements are selected from the population at a uniform interval (e.g., every half-hour, every twentieth item); this is recommended for many Six Sigma measurement activities.