Six Sigma Quality Management Flashcards

Question 1

What does Six Sigma aim to achieve in a process?

Accepted Answer

Six Sigma aims to improve process performance by reducing variation and eliminating defects, so that output consistently meets customer requirements. It is a disciplined, data-driven approach that uses statistical tools to find the causes of problems rather than relying on opinion. Organizations use it to lower costs, shorten cycle times, and raise customer satisfaction.

Question 2

What does the Greek letter sigma represent in this methodology?

Accepted Answer

In this methodology, sigma is the statistical symbol for standard deviation, which measures how spread out data points are around the average. A lower standard deviation means less variation. The sigma level of a process indicates how many standard deviations fit between the process mean and the nearest specification limit.

Question 3

What is a defect in Six Sigma terms?

Accepted Answer

A defect is any output or characteristic that fails to meet a specified customer requirement, such as a part outside its tolerance, a late delivery, or an incorrect invoice. Defects are counted against a defined standard, so teams must first agree on what counts as acceptable. Clear definitions prevent disagreement during measurement.

Question 4

What is the difference between a defect and a defective unit?

Accepted Answer

A defect is a single nonconforming characteristic, while a defective unit is an item that contains at least one defect. One unit can have several defects, so counting defects and counting defective units can produce different totals. Six Sigma practitioners choose the measure that matches the question being asked.

Question 5

What is a defect opportunity and why does it matter?

Accepted Answer

A defect opportunity is any chance within a product or process to fail a requirement. A single invoice may have several opportunities, such as correct amount, correct date, and correct account code. Counting opportunities lets teams compare processes of different complexity fairly, which is the basis for defects per million opportunities.

Question 6

What does DPMO stand for, and how is it calculated?

Accepted Answer

DPMO stands for defects per million opportunities. It is calculated by dividing the total number of defects by the total number of opportunities, then multiplying by one million. For example, 25 defects across 5,000 units with 4 opportunities each gives 25 divided by 20,000, times one million, which equals 1,250 DPMO.

Question 7

What defect rate does the classic Six Sigma target of 3.4 DPMO represent?

Accepted Answer

The classic Six Sigma target of 3.4 DPMO corresponds to about 3.4 defects per million opportunities after allowing for a long-term shift of 1.5 standard deviations in the process mean. It is a convention used to express world class performance, not a result that every process can or should reach.

Question 8

Why do Six Sigma teams focus on the customer's view of quality?

Accepted Answer

Six Sigma teams focus on the customer's view because quality is defined by what the customer needs and will accept, not by internal preferences. Requirements are gathered through voice of the customer methods such as interviews and complaint analysis, then translated into critical to quality characteristics that can be measured.

Question 9

What do the letters in the DMAIC roadmap stand for?

Accepted Answer

The letters in DMAIC stand for Define, Measure, Analyze, Improve, and Control. It is the standard five phase roadmap for improving an existing process that is not meeting requirements. Each phase has specific goals, tools, and decision gates, so teams move forward only when the current phase's outputs are complete.

Question 10

What happens during the Define phase of DMAIC?

Accepted Answer

During the Define phase, the team states the problem, sets the project scope and goals, identifies the customer and critical to quality requirements, and maps the high level process, often with a SIPOC diagram. A project charter records the business case, the team members, and the timeline.

Question 11

What is the main purpose of the Measure phase in DMAIC?

Accepted Answer

The main purpose of the Measure phase is to understand how the current process performs by collecting reliable data on key outputs and inputs. Teams validate the measurement system first, so they know the data can be trusted, and then establish a baseline sigma level or defect rate.

Question 12

How does the Analyze phase differ from the Improve phase?

Accepted Answer

The Analyze phase finds and confirms the root causes of the problem, using data and statistical tests to separate likely causes from trivial ones. The Improve phase then designs, tests, and implements solutions that address those confirmed causes. Analyze asks why the problem happens, while Improve asks what change will reliably remove it.

Question 13

Why is the Control phase important after improvements are made?

Accepted Answer

The Control phase protects gains by making sure the improved process keeps performing after the project team leaves. Teams use control plans, standard operating procedures, and control charts with response rules to catch drift early. Without these safeguards, processes tend to slide back toward their old behavior, and the benefits of the project are lost.

Question 14

What is DMADV and when is it typically used?

Accepted Answer

DMADV stands for Define, Measure, Analyze, Design, and Verify, and it is typically used to create a new product, service, or process, or to redesign one so completely that existing improvement methods are not suitable. Its design phases aim to build quality in from the start rather than fix defects after they appear.

Question 15

What does the Design phase accomplish in DMADV?

Accepted Answer

The Design phase develops and compares alternative concepts for the new product or process, then selects a design that meets the critical to quality requirements. Teams often use tools such as quality function deployment, which links customer needs to design features, and simulations to predict performance before building anything.

Question 16

How does the Verify phase in DMADV confirm a design is ready?

Accepted Answer

The Verify phase confirms that the design performs as intended under realistic conditions before full launch. Teams usually run pilot tests, check the design against customer requirements, and evaluate capability using the measurement data collected earlier. If results fall short, the team returns to earlier phases rather than launching a flawed design.

Question 17

What is the difference between common cause and special cause variation?

Accepted Answer

Common cause variation is the natural, random noise built into a stable process, while special cause variation comes from a specific, identifiable source that is not normally part of the process. A stable process shows only common cause variation. Special causes call for investigation, while common cause variation calls for process redesign.

Question 18

What is a control chart and what does it show?

Accepted Answer

A control chart is a time ordered plot of process data with a center line for the average and upper and lower control limits that reflect the process's natural variation. Points outside the limits, or unusual patterns within them, signal that a special cause may be affecting the process and deserves investigation.

Question 19

What is the difference between control limits and specification limits?

Accepted Answer

Control limits are calculated from the process's own data and show what the process naturally does, while specification limits come from customer requirements or engineering needs and show what is acceptable. A process can be in control yet still produce defects if its natural variation extends beyond specification limits.

Question 20

What does a process capability index tell a team about performance?

Accepted Answer

A process capability index compares the spread of a stable process with the width of its specification limits. Cp considers spread alone, while Cpk also reflects how well the mean is centered between the limits. These indices assume the process is stable and roughly normally distributed, so they should be checked first.

Question 21

What is a Pareto chart used for in Six Sigma?

Accepted Answer

A Pareto chart is a bar chart that orders problem categories from largest to smallest frequency or cost. It helps teams see the vital few causes that account for most of the total impact. It is widely used during Define and Analyze to prioritize projects and root causes.

Question 22

What is a measurement system analysis and why is it performed?

Accepted Answer

Measurement system analysis is a study that evaluates how much of the variation in collected data comes from the measurement process itself. It confirms that data can be trusted before teams use it to make decisions. A common method is gauge repeatability and reproducibility, which separates equipment variation from operator variation.

Question 23

What does the equation Y equals f of X represent in Six Sigma?

Accepted Answer

The equation Y equals f of X expresses the idea that an output of interest, Y, depends on a set of input variables, X, through some function. Y is the key output or critical to quality characteristic the business cares about, and the X values are the process inputs that drive it.

Question 24

What is the purpose of a histogram in process analysis?

Accepted Answer

A histogram groups measured data into intervals and shows how often values fall within each one, revealing the shape, center, and spread of the distribution. Teams use it to check whether data looks roughly normal, to spot skewness, outliers, or multiple peaks.

Question 25

What is a SIPOC diagram and when is it used?

Accepted Answer

A SIPOC diagram is a high level map that lists the suppliers, inputs, process steps, outputs, and customers of a process. It is used mainly during the Define phase to establish the project scope and clarify who provides what to whom. Because it stays at a high level, it helps teams agree on boundaries before detailed process mapping begins.

Question 26

How does a fishbone diagram help a team find possible causes?

Accepted Answer

A fishbone diagram, also called a cause and effect diagram, organizes possible causes of a problem into categories such as methods, machines, materials, people, measurements, and environment. The problem is written at the head of the fish, and branches show causes grouped under each category.

Question 27

How does the 5 Whys technique help identify root causes?

Accepted Answer

The 5 Whys technique asks why a problem occurred, then asks why each answer happened, repeating until the team reaches a root cause. Each answer must be supported by evidence rather than assumption. It can stop too early, so teams often verify the result with data.

Question 28

What is the purpose of Failure Mode and Effects Analysis in a project?

Accepted Answer

Failure Mode and Effects Analysis is a structured method for identifying the ways a product or process can fail, the effects of each failure, and the causes behind them. Teams score severity, occurrence, and detection, and multiply them to get a risk priority number that ranks where preventive action is most needed.

Question 29

What is a designed experiment and why is it useful?

Accepted Answer

A designed experiment is a planned test in which several input factors are deliberately changed in a structured pattern to observe their effects on an output. It is useful because it reveals main effects and interactions efficiently, showing how factors work together rather than one at a time.

Question 30

What is a hypothesis test and what does a p value indicate?

Accepted Answer

A hypothesis test compares sample data against a null hypothesis, usually a claim of no difference or no effect. The p value is the probability of observing results at least as extreme as the sample data if the null hypothesis were true. A small p value provides evidence against the null hypothesis.

Question 31

What is the difference between a Type I and a Type II error?

Accepted Answer

A Type I error occurs when a team rejects a true null hypothesis. A Type II error occurs when a team fails to reject a false null hypothesis, missing an effect that is really there. Type I risk is set by the significance level, while Type II risk depends on sample size and effect size.

Question 32

What is a regression analysis used for in Six Sigma?

Accepted Answer

Regression analysis models the relationship between a continuous output and one or more input variables, so teams can estimate how much the output changes when an input changes. It helps confirm which X variables truly drive Y and supports prediction of performance under different settings.

Question 33

What do the Six Sigma belt colors generally indicate about a person's role?

Accepted Answer

Belt colors indicate a practitioner's level of training and responsibility, though the exact names and requirements vary by organization. Yellow and green belts typically receive basic training and support projects part time, while black belts lead full time improvement projects and mentor others. Master black belts coach black belts across the organization.

Question 34

What responsibilities does a Six Sigma champion typically carry in an organization?

Accepted Answer

A Six Sigma champion is typically a senior leader who sponsors improvement projects, aligns them with business strategy, and allocates resources. Champions help select projects and clear organizational obstacles. Their visible support signals that quality improvement is a priority for the whole organization, not only for the project teams.

Question 35

What does a Six Sigma black belt do day to day?

Accepted Answer

A black belt usually leads one or more improvement projects full time, guiding the team through the DMAIC or DMADV roadmap and applying statistical tools correctly. They coach green belts, facilitate workshops, analyze data, and present findings to senior leaders. Black belts also build the skills of others, so that improvement capability remains inside the organization after the project ends.

Question 36

What is a project charter and what should it include?

Accepted Answer

A project charter is a short document that formalizes an improvement project, stating the problem, goal, scope, team members, sponsor, and timeline. It also records the business case, expected benefits, and key constraints or assumptions. A clear charter gives the team authority to work and gives leaders a reference point for reviewing progress.

Question 37

How do teams use the voice of the customer to guide improvement?

Accepted Answer

Teams use the voice of the customer by collecting needs, expectations, and complaints through interviews, surveys, focus groups, and complaint records. These statements are then translated into measurable critical to quality requirements that guide the project's goals and measurements. Capturing customer language early prevents teams from optimizing internal measures that customers do not value.

Question 38

What is the purpose of a control plan in the Control phase?

Accepted Answer

A control plan documents how the improved process will be monitored and maintained, including which characteristics to measure, how often, by whom, using what method, and what action to take if results go out of bounds. It turns project learning into routine operating practice.

Question 39

What are common reasons improvement gains fade after a project ends?

Accepted Answer

Improvement gains often fade when teams lack a control plan, when ownership of the process is unclear, or when people revert to old habits because training and documentation were incomplete. Leaders may shift attention to new priorities too soon. Sustaining results requires ongoing measurement, clear accountability, and regular review of key metrics.

Question 40

How do Six Sigma and Lean methods differ and complement each other?

Accepted Answer

Six Sigma focuses mainly on reducing variation and defects using statistical analysis, while Lean focuses on eliminating waste and improving flow. Variation often creates waste, and waste can hide variation. Many organizations combine them into Lean Six Sigma, using Lean tools for flow and Six Sigma tools for reliable results.

Six Sigma Quality Management Flashcards

1Core Six Sigma Concepts

2DMAIC and DMADV Roadmaps

3Variation and Process Measurement

4Analysis and Improvement Tools

5Roles, Implementation and Sustainment

Learning Resources