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PECB Six Sigma Yellow Belt study materials
PECB Six Sigma Yellow Belt study resources

PECB Six Sigma Yellow Belt practice questions

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Question 1Principles and foundations of Lean Six Sigma

In Lean Six Sigma, what does the term 'sigma level' express about a process?

  1. The percentage of employees who have completed statistical training
  2. The number of defects a process is contractually allowed to deliver
  3. How many standard deviations fit between the process mean and the nearest specification limit Correct answer.
  4. The total number of improvement projects a department runs per year

Explanation

Sigma level measures process capability by counting how many standard deviations separate the process mean from the closest specification limit. A higher sigma level means fewer defects per million opportunities, so the process is more capable and less variable.

Question 2Principles and foundations of Lean Six Sigma

A process operates at a sigma level of 6. Approximately how many defects per million opportunities does this correspond to in the classic Six Sigma model (with the 1.5 sigma shift)?

  1. 3.4 Correct answer.
  2. 66,807
  3. 6,210
  4. 233

Explanation

The classic Six Sigma benchmark is 3.4 defects per million opportunities, derived from a 1.5 sigma long-term shift. This is the reference point used throughout Six Sigma literature to describe near-perfect process performance.

Question 3Principles and foundations of Lean Six Sigma

Which statement best captures the core idea of Lean thinking?

  1. Increase inspection frequency at the end of the line to catch defects
  2. Maximize the number of steps in a process so that each step can be inspected
  3. Systematically identify and eliminate activity that does not add value for the customer Correct answer.
  4. Reduce variation in process output by controlling causes statistically

Explanation

Lean thinking focuses on value as defined by the customer and on removing waste, meaning any activity that consumes resources without creating value. Six Sigma complements this by attacking variation, while Lean addresses flow and non-value-adding steps.

Question 4Principles and foundations of Lean Six Sigma

Which of the following is classified as one of the classic Lean wastes?

  1. Benchmarking
  2. Standardization
  3. Overproduction Correct answer.
  4. Calibration

Explanation

Overproduction, making more or earlier than the customer needs, is one of the classic Lean wastes because it triggers inventory, waiting, and handling costs. Standardization, benchmarking, and calibration are practices or controls, not categories of waste.

Question 5Principles and foundations of Lean Six Sigma

A production team holds more raw material than needed because a supplier offers quantity discounts. Which Lean waste does this situation primarily represent?

  1. Inventory Correct answer.
  2. Waiting
  3. Overprocessing
  4. Motion

Explanation

Excess raw material held beyond what the process needs is inventory waste, which ties up capital and hides quality problems. Motion refers to people movement, waiting refers to idle time, and overprocessing refers to doing more work than the customer values.

Question 6Principles and foundations of Lean Six Sigma

What is the primary purpose of the DMAIC roadmap in Six Sigma?

  1. To document the financial audit trail required by regulators
  2. To design a brand-new product from concept to launch
  3. To replace statistical process control charts with management reviews
  4. To structure improvement work on existing processes from problem definition through control Correct answer.

Explanation

DMAIC (Define, Measure, Analyze, Improve, Control) is the structured methodology for improving processes that already exist. Design for Six Sigma and DMADV are used when a new process or product must be created instead.

Question 7Principles and foundations of Lean Six Sigma

During which DMAIC phase is a process map typically created to understand how the current process actually operates?

  1. Control
  2. Measure Correct answer.
  3. Define
  4. Improve

Explanation

Detailed process mapping usually occurs in the Measure phase, where the team documents the current state and gathers baseline data. The Define phase sets scope and the problem statement, while Improve and Control address changes and sustainment.

Question 8Principles and foundations of Lean Six Sigma

In a Six Sigma project, what is the role of the process owner (often called the sponsor or champion at leadership level)?

  1. To provide resources, remove barriers, and ensure improvements are sustained in the business Correct answer.
  2. To personally collect all measurement data used in the Analyze phase
  3. To audit the project team against the DMAIC phase gate checklist
  4. To run the statistical software and interpret every hypothesis test

Explanation

The sponsor or champion provides authority, resources, and organizational support, and helps ensure gains are institutionalized. Data collection and statistical analysis are typically performed by Belt-level practitioners and the project team.

Question 9Principles and foundations of Lean Six Sigma

Which description best matches the responsibilities of a Six Sigma Green Belt?

  1. Leads improvement projects part-time within their own area while continuing their regular job Correct answer.
  2. Owns the process after the project and approves capital expenditure
  3. Sets the enterprise-wide deployment strategy and selects which business units to fund
  4. Provides statistical consulting only and never leads a project

Explanation

A Green Belt typically leads projects on a part-time basis in addition to regular duties and may support Black Belts on larger efforts. Deployment strategy and funding decisions belong to leadership, such as champions and deployment leaders.

Question 10Principles and foundations of Lean Six Sigma

A Yellow Belt is asked to support a project team. Which activity is most appropriate for a Yellow Belt to perform?

  1. Participate in process mapping, collect data as directed, and help implement improvements Correct answer.
  2. Approve the project charter and release the project budget
  3. Perform a multi-vari study and determine which factors are statistically significant
  4. Redesign the measurement system and validate it with a gauge R&R study

Explanation

Yellow Belts work as team members, contributing process knowledge, supporting data collection, and helping implement and sustain improvements. Advanced statistical studies and charter approval sit with more senior Belts or leadership.

Question 11Principles and foundations of Lean Six Sigma

What is the main purpose of a project charter in a Six Sigma initiative?

  1. To define the problem, scope, goals, team, and boundaries of the project Correct answer.
  2. To record the detailed statistical results of every hypothesis test
  3. To replace the need for a business case and stakeholder approval
  4. To list every defect found during the Control phase

Explanation

The charter authorizes the project and clarifies the problem statement, scope, objectives, team roles, and constraints. It aligns stakeholders before work begins and prevents scope creep during later phases.

Question 12Principles and foundations of Lean Six Sigma

A team writes a problem statement that says 'Reduce defects by improving operator attitude.' What is the main weakness of this statement for a Six Sigma project?

  1. It fails to include the sigma level of the process
  2. It does not mention the DMAIC phase names
  3. It proposes a solution and blames people instead of describing an observable gap Correct answer.
  4. It is too long to fit on the charter template

Explanation

A good problem statement describes an observable, quantified gap between current and desired performance without prescribing a cause or solution. Attributing defects to attitude is an unverified assumption that biases the investigation.

Question 13Principles and foundations of Lean Six Sigma

In Six Sigma terminology, what is a 'critical to quality' (CTQ) characteristic?

  1. A feature of the product or service that measurably matters to the customer Correct answer.
  2. A statistical test used to compare two process means
  3. The internal cost target set for a manufacturing cell
  4. Any process input that the engineering department can control directly

Explanation

CTQ characteristics translate customer needs into measurable requirements that the process must satisfy. They form the basis for defining defects and setting specification limits in the Measure phase.

Question 14Principles and foundations of Lean Six Sigma

A call center records that customers most often complain about long hold times. How should this voice-of-customer input be translated for a Six Sigma project?

  1. Record it as an assumption in the charter without measurement
  2. Ignore it because complaints are subjective and cannot be measured
  3. Convert it into a measurable CTQ such as average hold time in seconds against a target Correct answer.
  4. Treat it as a root cause and immediately change the phone system

Explanation

Voice-of-customer statements must be translated into measurable requirements so performance can be quantified and defects defined. Average hold time against a target is an operational definition of the customer need.

Question 15Principles and foundations of Lean Six Sigma

Which statement correctly describes the relationship between Lean and Six Sigma?

  1. Lean focuses on speed and waste reduction, while Six Sigma focuses on variation reduction and defect prevention Correct answer.
  2. Six Sigma eliminates the need for flow and pull systems
  3. Lean requires advanced statistical software, while Six Sigma does not
  4. Lean and Six Sigma are competing methodologies and cannot be combined

Explanation

Lean and Six Sigma address complementary problems: Lean improves flow and removes non-value-adding activity, while Six Sigma reduces variation and defects. Combining them lets organizations improve both speed and quality.

Question 16Principles and foundations of Lean Six Sigma

A process produces 12 defects across 4,000 opportunities. What is the defects per million opportunities (DPMO)?

  1. 3,000 Correct answer.
  2. 30,000
  3. 0.003
  4. 300

Explanation

DPMO equals defects divided by opportunities, multiplied by one million. Here 12 divided by 4,000 is 0.003, and multiplying by one million gives 3,000 DPMO.

Question 17Principles and foundations of Lean Six Sigma

Why does Six Sigma emphasize reducing variation rather than only meeting an average target?

  1. Averages are always calculated incorrectly in manufacturing data
  2. High variation causes output to fall outside specification limits even when the mean is on target Correct answer.
  3. Customers prefer variation because it gives them more product choices
  4. Variation reduction guarantees that the process mean will shift upward

Explanation

Even a process centered on target will produce defects if its spread is wide relative to the specification limits. Reducing variation narrows the output distribution and lowers the defect rate.

Question 18Principles and foundations of Lean Six Sigma

What does a process capability index such as Cp compare?

  1. The process mean to the customer complaint count
  2. The number of operators to the number of machines
  3. The specification width to the process spread, expressed in standard deviations Correct answer.
  4. The cost of poor quality to the project budget

Explanation

Cp relates the allowable specification width to six standard deviations of the process, measuring potential capability when the process is centered. Cpk additionally accounts for how far the mean is offset from the target.

Question 19Principles and foundations of Lean Six Sigma

A team is told that its process has a Cpk of 0.65. What does this indicate?

  1. The process is not capable and produces significant output outside specification Correct answer.
  2. The process mean is exactly centered with no variation
  3. The process has no specification limits defined
  4. The process is highly capable and needs no improvement

Explanation

A Cpk below 1.0 indicates that the process spread exceeds the specification width or the mean is offset, so output falls outside limits. Values of 1.33 or higher are commonly targeted for capable processes.

Question 20Principles and foundations of Lean Six Sigma

What is the purpose of a cost of poor quality (COPQ) analysis in a Six Sigma business case?

  1. To set the selling price of the product in the market
  2. To determine the purchase price of new statistical software
  3. To calculate the salary of each project team member
  4. To quantify the financial impact of defects, rework, scrap, and lost customer goodwill Correct answer.

Explanation

COPQ translates quality problems into financial terms so the project can be justified and prioritized against other opportunities. It typically includes internal and external failure costs such as scrap, rework, warranty, and lost business.

Question 21Principles and foundations of Lean Six Sigma

Which of the following best describes a 'hidden factory' in Lean Six Sigma terms?

  1. A production line that operates only during night shifts
  2. A supplier facility located outside the home country
  3. The extra work created by rework, sorting, and expediting that the formal process does not intend Correct answer.
  4. A plant that is not visible on the organization chart

Explanation

The hidden factory refers to the unplanned effort spent correcting, sorting, and expediting defective work. It consumes capacity and cost without adding customer value, and reducing it is a common improvement target.

Question 22Principles and foundations of Lean Six Sigma

A team uses a Pareto chart during a project. What does this tool help them do?

  1. Show the statistical correlation between two continuous variables
  2. Prioritize the few categories of problems that account for most of the effect Correct answer.
  3. Display the control limits of a process over time
  4. Demonstrate the cause-and-effect relationships among many inputs

Explanation

A Pareto chart orders categories by frequency or impact, illustrating the principle that a small number of causes usually produce most of the effect. It helps teams focus improvement effort where it will yield the greatest return.

Question 23Principles and foundations of Lean Six Sigma

A team wants to brainstorm and organize possible causes of a defect into categories such as machine, method, material, and people. Which tool is most appropriate?

  1. Histogram
  2. Control chart
  3. Fishbone (Ishikawa) diagram Correct answer.
  4. Run chart

Explanation

A fishbone diagram organizes brainstormed causes into categories to structure root cause investigation. It is often paired with a Pareto chart to prioritize which causes to verify with data.

Question 24Principles and foundations of Lean Six Sigma

Which statement about a run chart is accurate?

  1. It ranks defect categories from highest to lowest count
  2. It calculates the correlation coefficient between two variables
  3. It displays the frequency distribution of a variable using bars
  4. It plots data in time order and helps reveal trends, shifts, or unusual patterns Correct answer.

Explanation

A run chart shows measurements in chronological order so the team can see trends, shifts, and patterns over time. It is a simple starting point before applying formal control chart rules.

Question 25Principles and foundations of Lean Six Sigma

In the context of Six Sigma, what does 'defect opportunity' mean when calculating DPMO?

  1. A measurable chance for a nonconformity to occur in a unit of product or service Correct answer.
  2. The number of projects the organization can fund in a year
  3. A scheduled maintenance window on production equipment
  4. Any moment when an operator is available to inspect the product

Explanation

An opportunity is a specific point in the process or product where a defect could occur, such as a required characteristic or a service step. Counting opportunities correctly is essential because DPMO depends on the denominator.

Question 26Principles and foundations of Lean Six Sigma

Which sequence correctly orders the five phases of the DMAIC methodology?

  1. Define, Measure, Analyze, Improve, Correct
  2. Define, Measure, Analyze, Improve, Control Correct answer.
  3. Design, Measure, Analyze, Improve, Control
  4. Define, Monitor, Analyze, Improve, Control

Explanation

DMAIC stands for Define, Measure, Analyze, Improve and Control, and the phases are executed in that order. Each phase has defined deliverables that gate entry into the next phase.

Question 27Principles and foundations of Lean Six Sigma

A manufacturer wants to design a brand-new product and process so that capability targets are met before launch. Which Six Sigma methodology is intended for this situation?

  1. PDCA
  2. DMAIC
  3. A3 problem solving
  4. DMADV Correct answer.

Explanation

DMADV (Define, Measure, Analyze, Design, Verify) is the design-for-Six-Sigma roadmap used when a process does not yet exist or cannot be fixed to meet requirements. DMAIC assumes an existing process to improve.

Question 28Principles and foundations of Lean Six Sigma

In Six Sigma language, what does the term 'sigma level' express about a process?

  1. The ratio of rework cost to total revenue
  2. The percentage of employees trained at Green Belt level
  3. The number of standard deviations between the process mean and the nearest specification limit Correct answer.
  4. The total number of inspections performed per shift

Explanation

Sigma level counts how many standard deviations fit between the process mean and the closest specification limit, so it rises as defects fall. It is a shorthand for process capability expressed on a common scale.

Question 29Principles and foundations of Lean Six Sigma

Where did the Six Sigma methodology originate, and what was its initial focus?

  1. At Motorola, focused on reducing product defects in manufacturing Correct answer.
  2. At Toyota, focused on eliminating inventory waste
  3. At Ford, focused on assembly-line balancing
  4. At Xerox, focused on benchmarking competitor products

Explanation

Six Sigma was developed at Motorola in the 1980s as a statistical approach to reducing defects in manufacturing. It was later popularized by General Electric and extended to service and transactional processes.

Question 30Principles and foundations of Lean Six Sigma

A process operates at a Six Sigma level with the customary 1.5 sigma shift. Approximately how many defects per million opportunities does this correspond to?

  1. 66,807
  2. 6,210
  3. 3.4 Correct answer.
  4. 233

Explanation

A Six Sigma process with the conventional 1.5 sigma long-term shift is quoted at about 3.4 defects per million opportunities. This figure is the benchmark value widely used in Six Sigma training.

Question 31Principles and foundations of Lean Six Sigma

Which pairing of Lean thinking and Six Sigma is described correctly?

  1. Lean targets design of experiments, while Six Sigma targets workplace organization
  2. Lean targets variation, while Six Sigma targets inventory levels
  3. Lean targets speed and waste, while Six Sigma targets variation and defects Correct answer.
  4. Lean targets statistical process control, while Six Sigma targets value-stream mapping

Explanation

Lean concentrates on removing non-value-adding waste to improve flow and speed, whereas Six Sigma uses statistical methods to reduce variation and defects. Combining them lets a team improve both speed and consistency.

Question 32Principles and foundations of Lean Six Sigma

In Lean terminology, which of the following is classified as one of the classic forms of waste?

  1. Overproduction Correct answer.
  2. Poka-yoke
  3. Visual management
  4. Standardization

Explanation

Overproduction is one of the classic wastes because making more or earlier than the customer needs consumes resources and hides other problems. Standardization, visual management and poka-yoke are countermeasures rather than wastes.

Question 33Principles and foundations of Lean Six Sigma

What does the Lean concept of 'value' depend on most directly?

  1. What the finance department budgets for the year
  2. What the production supervisor can schedule conveniently
  3. What the customer is willing to pay for Correct answer.
  4. What the engineering team finds technically interesting

Explanation

In Lean, value is defined from the customer's perspective: only activities the customer would pay for add value. Everything else is waste to be reduced or eliminated.

Question 34Principles and foundations of Lean Six Sigma

A service team maps each step of its loan approval process and marks which steps the customer would pay for. What Lean analysis are they performing?

  1. Hypothesis testing of defect rates
  2. Design of experiments on approval times
  3. Measurement system analysis of the reviewers
  4. Value-added analysis of the process steps Correct answer.

Explanation

Classifying steps as value-adding or non-value-adding is value-added analysis, a core Lean activity used to identify waste. It precedes efforts to streamline or remove the non-value-adding steps.

Question 35Principles and foundations of Lean Six Sigma

What is the primary purpose of a value-stream map in a Lean Six Sigma project?

  1. To document the audit findings of the quality department
  2. To calculate the Cp and Cpk of each individual machine
  3. To list every employee who touches the product and their certification level
  4. To show material and information flow and expose where lead time and waste accumulate Correct answer.

Explanation

A value-stream map depicts the flow of material and information across the whole value stream and highlights delay and waste. It is used to identify where lead time is lost and where improvement should focus.

Question 36Principles and foundations of Lean Six Sigma

A warehouse team reorganizes tools, sorts items, and labels storage locations so that anyone can find what is needed. Which Lean practice does this illustrate?

  1. Kanban pull scheduling
  2. 5S workplace organization Correct answer.
  3. Total productive maintenance
  4. Single-minute exchange of die

Explanation

5S (sort, set in order, shine, standardize, sustain) organizes the workplace so items are easy to find and abnormalities are visible. Sorting and labeling storage locations are direct 5S actions.

Question 37Principles and foundations of Lean Six Sigma

In Lean Six Sigma, what is the purpose of a kaizen event?

  1. To complete a full DMAIC project with extensive data collection over several months
  2. To make focused, rapid improvements to a defined process over a short, dedicated period Correct answer.
  3. To certify new Black Belts through an examination process
  4. To replace statistical analysis with employee opinion surveys

Explanation

A kaizen event, sometimes called a kaizen blitz, brings a team together for a short intensive period to implement focused improvements. It contrasts with longer DMAIC projects that rely on extended data collection and analysis.

Question 38Principles and foundations of Lean Six Sigma

What does the Lean principle of 'pull' mean in a production or service process?

  1. Each department pushes work forward as soon as it is finished
  2. Production runs at full capacity regardless of customer orders
  3. Downstream demand triggers replenishment rather than work being pushed on a forecast Correct answer.
  4. Inventory is maximized so that no order is ever delayed

Explanation

In a pull system, a downstream signal authorizes upstream work or replenishment, so output is tied to actual demand. This reduces overproduction and excess inventory compared with push scheduling.

Question 39Principles and foundations of Lean Six Sigma

A Yellow Belt notices that a process step is performed only because of a legacy rule that no customer requires. Which Lean waste category does this step most directly represent?

  1. Transportation
  2. Over-processing Correct answer.
  3. Waiting
  4. Motion

Explanation

Over-processing means doing more work to a product or service than the customer values, such as unnecessary steps, approvals or inspections. A legacy step that adds no customer value fits this category.

Question 40Principles and foundations of Lean Six Sigma

Which statement best captures the concept of 'takt time'?

  1. The total downtime recorded over a shift
  2. The maximum speed a machine can physically run
  3. The available production time divided by customer demand rate Correct answer.
  4. The average number of defects per unit produced

Explanation

Takt time is the pace at which a process must complete one unit to meet customer demand, calculated as available time divided by demand. It sets the rhythm the process should be designed to match.

Question 41Principles and foundations of Lean Six Sigma

A process has an observed cycle time of 40 seconds per unit, and takt time is 30 seconds per unit. What does this comparison indicate?

  1. The process cannot keep pace with demand and needs cycle time reduced or capacity added Correct answer.
  2. The process is producing exactly at the rate customers require
  3. The process is overstaffed and should slow down
  4. The process has no variation in its output

Explanation

When cycle time exceeds takt time, the process is slower than the pace needed to satisfy demand. The team must reduce cycle time, add capacity, or otherwise close the gap.

Question 42Principles and foundations of Lean Six Sigma

What is the main purpose of a Kanban card in a Lean process?

  1. To record the inspection results for each finished unit
  2. To authorize overtime hours for the shift
  3. To signal that downstream consumption has created a need for upstream replenishment Correct answer.
  4. To document the training record of each operator

Explanation

A Kanban card is a visual pull signal that tells an upstream step to produce or deliver more because downstream has consumed material. It limits work in process and prevents overproduction.

Question 43Principles and foundations of Lean Six Sigma

Which statement correctly distinguishes common-cause variation from special-cause variation?

  1. Common-cause variation is always caused by operators, while special-cause variation is always caused by suppliers
  2. Common-cause variation can be removed only by inspecting every unit, while special-cause variation cannot be addressed
  3. Common-cause variation is inherent in the process, while special-cause variation arises from identifiable, unusual events Correct answer.
  4. Common-cause variation is unpredictable, while special-cause variation is the normal noise of the process

Explanation

Common-cause variation is the routine, inherent spread produced by the process design and its many small inputs. Special-cause variation comes from identifiable events or assignable causes and signals that something has changed.

Question 44Principles and foundations of Lean Six Sigma

A control chart shows a point beyond the upper control limit. What is the appropriate interpretation?

  1. The process is performing better than expected and needs no action
  2. The control limits must be recalculated to include the point
  3. The measurement system has automatically failed
  4. A special cause is likely present and the process should be investigated Correct answer.

Explanation

A point outside the control limits is a standard signal of special-cause variation, so the team should investigate what changed at that time. Reacting to every common-cause fluctuation, by contrast, tends to increase variation.

Question 45Principles and foundations of Lean Six Sigma

Why is the concept of 'cost of poor quality' important to a Six Sigma business case?

  1. It quantifies the financial loss from defects, rework, scrap and warranty so improvement benefits can be justified Correct answer.
  2. It records the salaries of the quality assurance staff only
  3. It calculates the depreciation of production equipment
  4. It measures the purchase price of raw materials from suppliers

Explanation

Cost of poor quality captures the money lost to internal and external failures, appraisal and prevention activities, making the financial impact of defects visible. This helps justify a project by showing the recoverable value.

Question 46Principles and foundations of Lean Six Sigma

A team states its goal as 'become world class in quality.' Why is this goal weak for a Six Sigma project?

  1. It is too focused on a single numerical metric
  2. It lacks a measurable target, baseline and timeframe needed to verify improvement Correct answer.
  3. It cannot be communicated to senior management
  4. It requires data collection that Six Sigma does not permit

Explanation

A usable Six Sigma goal must be specific and measurable, with a baseline, a target and a deadline, so progress can be verified. 'World class' is a vague aspiration that cannot be tested.

Question 47Principles and foundations of Lean Six Sigma

A hospital wants to reduce patient waiting time. Which measure best represents a 'critical to quality' characteristic in this context?

  1. Total square meters of the waiting room
  2. Minutes a patient waits before being seen by a clinician Correct answer.
  3. Percentage of staff who completed orientation
  4. Number of staff meetings held each week

Explanation

A CTQ characteristic translates a customer need into a measurable requirement, and patients value short waiting time. Measuring minutes waited directly reflects that requirement.

Question 48Principles and foundations of Lean Six Sigma

In a Lean Six Sigma context, what does 'poka-yoke' refer to?

  1. A chart that tracks defects over time
  2. A schedule for preventive maintenance
  3. A device or design that prevents an error from being made or passed on Correct answer.
  4. A method for calculating return on investment

Explanation

Poka-yoke means mistake-proofing: designing a step so that an error is either impossible or immediately detected. It addresses defects at the source rather than relying on inspection.

Question 49Principles and foundations of Lean Six Sigma

Which statement best describes the relationship between a process and a system in Lean Six Sigma thinking?

  1. A system is simply another word for a single process step
  2. A process is the same as a system and the terms are interchangeable
  3. A system refers only to the software used to record data
  4. A system is a set of interdependent processes whose combined performance can differ from the sum of the parts Correct answer.

Explanation

Systems thinking recognizes that processes interact, so optimizing one process in isolation can harm overall performance. Improvement should consider how the interacting processes affect the whole system.

Question 50Principles and foundations of Lean Six Sigma

A team reduces the average processing time of a service step but customer complaints rise because the spread of times has widened. Which principle does this illustrate?

  1. Reducing variation matters as much as shifting the average Correct answer.
  2. Faster processes always improve customer satisfaction
  3. Complaints are unrelated to process performance
  4. Averages are the only measure that matters

Explanation

Six Sigma emphasizes that customers experience both the average and the spread; a wider spread means more extreme outcomes even if the mean improves. Reducing variation is therefore central to satisfying requirements consistently.