Title: Six Sigma Basics — LearnCoachAssist

Q: What does DMAIC stand for in Six Sigma?
A: Define, Measure, Analyze, Improve, Control. It is the data-driven improvement cycle used for projects aimed at improving existing processes.

Q: Which Six Sigma belt level is responsible for leading project teams?
A: Green Belts. They lead smaller improvement projects while working part-time on Six Sigma, typically under the guidance of a Black Belt.

Q: What is the purpose of a Fishbone diagram in the Analyze phase?
A: Also called an Ishikawa or cause-and-effect diagram, it helps teams brainstorm and categorize potential root causes of a problem, often grouped into the 6 Ms: Man, Machine, Material, Method, Measurement, and Mother Nature.

Q: What does a p-chart monitor?
A: A p-chart monitors the proportion of defective items in subgroups of varying size, tracking attribute (pass/fail) data over time.

Q: Define process capability index Cp.
A: Cp = (USL - LSL) / (6 * standard deviation). It measures the potential capability of a process by comparing specification width to process spread, ignoring centering.

Q: What is Cpk and how does it differ from Cp?
A: Cpk accounts for process centering. It is the minimum of (USL - mean)/(3σ) and (mean - LSL)/(3σ). Cp assumes perfect centering; Cpk reflects actual performance.

Q: Name the seven classic types of muda (waste) in lean.
A: Defects, Overproduction, Waiting, Non-utilized talent, Transportation, Inventory, Motion, and Extra processing (often remembered as DOWNTIME).

Q: What is the Voice of Customer (VOC)?
A: VOC is the process of capturing customers' expectations, preferences, and requirements for a product or service, typically through surveys, interviews, focus groups, and complaint data.

Q: What is a Type I error in hypothesis testing?
A: A Type I error occurs when the null hypothesis is rejected even though it is true. Its probability equals the significance level, alpha (α).

Q: What is the Six Sigma defect rate goal?
A: 3.4 defects per million opportunities (DPMO), corresponding to a process operating at ±6 standard deviations between the specification limits.

Q: What does an X-bar chart display?
A: An X-bar chart plots the subgroup (sample) means over time to monitor the central tendency of a process, with center line and upper/lower control limits calculated from the subgroup averages.

Q: What is the difference between common cause and special cause variation?
A: Common cause variation is inherent to the process and predictable; special cause variation comes from external sources and creates unpredictable signals. Control charts help distinguish the two.

Q: What is a Pareto chart used for?
A: A Pareto chart is a bar graph that displays categories of problems in descending order with a cumulative percentage line, helping identify the vital few causes contributing to most issues (80/20 rule).

Q: Define Rolled Throughput Yield (RTY).
A: RTY is the probability that a single unit passes through an entire multi-step process defect-free. It is calculated as the product of individual step yields: RTY = Y1 × Y2 × ... × Yn.

Q: What is a Black Belt's primary role?
A: Black Belts are full-time Six Sigma leaders who drive complex projects, coach Green Belts, apply advanced statistical tools, and typically complete projects generating significant financial savings.

Q: What is a Champion in a Six Sigma organization?
A: A Champion is a senior executive who sponsors and removes barriers for projects, aligns Six Sigma with business strategy, and ensures resources are available. They do not run projects day-to-day.

Q: What does an R-chart monitor?
A: An R-chart monitors process variability by plotting the range (max-min) of each subgroup over time, used together with the X-bar chart for variables data.

Q: What is the difference between accuracy and precision?
A: Accuracy is how close measurements are to the true value; precision is how close repeated measurements are to each other. A process can be precise but inaccurate (off-target).

Q: What is the central limit theorem's importance to Six Sigma?
A: It states that the distribution of sample means approaches a normal distribution as sample size grows, regardless of population shape. This allows X-bar charts and many statistical inferences to assume normality.

Q: What is a SIPOC diagram?
A: Suppliers, Inputs, Process, Outputs, Customers. A SIPOC is a high-level process map created in the Define phase to identify all relevant elements of a project before detailed work begins.

Q: What is Gage R&R used for?
A: Gage R&R (Repeatability and Reproducibility) studies quantify the measurement system variation as a percentage of total variation or tolerance, assessing whether a gauge is suitable for the process.

Q: What is the difference between an Xbar-R and Xbar-S chart?
A: Xbar-R uses subgroup ranges and is preferred when subgroup size n ≤ 10. Xbar-S uses subgroup standard deviations and is more accurate when n > 10.

Q: What is a kano model used for in VOC?
A: The Kano model categorizes customer requirements into Must-be, One-dimensional, and Attractive features, helping prioritize which attributes deliver the most satisfaction or competitive advantage.

Q: Define DPMO.
A: Defects Per Million Opportunities. DPMO = (Number of defects / (Number of units × Number of opportunities per unit)) × 1,000,000. It standardizes defect rates across processes with different complexity.

Q: What is a Master Black Belt?
A: A Master Black Belt is a technical expert and leader of Black Belts who typically trains and mentors, ensures consistency in methodology, and champions Six Sigma strategy across multiple business areas.

Q: What does ANOVA test for?
A: Analysis of Variance tests whether the means of three or more groups differ significantly by comparing between-group variation to within-group variation, producing an F-statistic.

Q: What is a control chart's upper control limit typically set at?
A: UCL is generally set at 3 standard deviations from the center line (mean). For an X-bar chart, UCL = X-double-bar + A2 × R-bar, providing a 99.73% confidence band assuming common cause variation only.

Q: What is a t-test used for?
A: A t-test compares the means of one or two groups to determine whether differences are statistically significant. Variants include one-sample, two-sample (independent), and paired t-tests.

Q: What is the Improve phase goal?
A: The Improve phase generates, pilots, and implements solutions that address root causes identified in earlier phases. It focuses on selecting solutions that reduce defects, variation, or cycle time and validating results with data.

Q: What is overproduction as a lean waste?
A: Producing more, sooner, or faster than the customer requires. It is considered the worst waste because it leads to excess inventory, hides other problems, and increases costs.

Q: Define sigma level.
A: Sigma level is the number of standard deviations between the process mean and the nearest specification limit. A 6σ process has only 3.4 DPMO; lower sigma levels indicate higher defect rates and worse capability.

Q: What is a CTQ tree?
A: Critical-to-Quality tree. It translates high-level customer needs (VOC) into specific, measurable, actionable requirements. Steps: customer need → CTQ → measurable requirement → specification.

Q: What is the purpose of a histogram?
A: A histogram shows the frequency distribution of continuous data, revealing shape (normal, skewed, bimodal), center, spread, and presence of outliers—useful in the Measure and Analyze phases.

Q: What is regression analysis in Six Sigma?
A: Regression models the relationship between a dependent response variable (Y) and one or more independent predictors (X). It quantifies how changes in X affect Y and is widely used for optimization.

Q: What does a normal probability plot show?
A: A normal probability plot graphs data points against expected normal quantiles. A roughly straight line indicates the data are approximately normally distributed; curvature suggests non-normality.

Q: Define throughput time.
A: Throughput time (or cycle time) is the total time a unit spends in a process from start to finish, including value-added and non-value-added activities. Reducing it improves responsiveness and lowers WIP.

Q: What is a Design of Experiments (DOE)?
A: DOE is a structured method to identify cause-and-effect relationships by intentionally varying multiple factors simultaneously. It enables modeling, optimization, and confirmation of improvements efficiently.

Q: What is FMEA?
A: Failure Mode and Effects Analysis. A systematic method to identify potential failure modes in a process or product, score Severity, Occurrence, and Detection to compute a Risk Priority Number, then prioritize actions.

Q: What is the difference between validation and verification?
A: Verification confirms a product or process meets specified requirements (are we building the product right?). Validation confirms it meets the actual user need (are we building the right product?).

Q: What is hypothesis testing's p-value?
A: The p-value is the probability of obtaining test results at least as extreme as observed, assuming the null hypothesis is true. If p < α (typically 0.05), reject H0 and accept the alternative.

Q: What does SIPOC stand for in the Define phase?
A: Suppliers, Inputs, Process, Outputs, Customers. It is a high-level process map used to identify all relevant elements of a project before detailed measurement begins.

Q: What is the formula for DPMO?
A: DPMO = (Number of Defects × 1,000,000) / (Number of Units × Number of Opportunities per Unit). It expresses defects per million opportunities for benchmarking.

Q: What is the role of a Green Belt in Six Sigma?
A: A Green Belt is a part-time Six Sigma practitioner who supports Black Belts on projects, leads smaller improvement efforts, and applies DMAIC within their functional area.

Q: What does a c-chart monitor?
A: A c-chart monitors the count of defects per unit when the sample size is constant. It is used for nonconformities, not nonconforming units, and assumes Poisson-distributed data.

Q: What is the difference between Cp and Cpk?
A: Cp measures potential process capability assuming the process is centered on specification. Cpk measures actual capability, accounting for any shift of the mean toward one specification limit.

Q: What is a confidence interval in hypothesis testing?
A: A confidence interval is a range of values, derived from sample data, that likely contains the true population parameter with a stated probability (e.g., 95%). Wider intervals indicate more uncertainty.

Q: What is the formula for Process Capability Index Cpk?
A: Cpk = min[(USL - μ)/3σ, (μ - LSL)/3σ]. It measures how well the process mean stays within specifications relative to process spread, with values below 1.33 indicating poor capability.

Q: What is Muda in Lean?
A: Muda is the Japanese term for waste—any activity that consumes resources without creating value for the customer. The original Toyota system identified seven types, later expanded to eight.

Q: What is the purpose of the Control phase in DMAIC?
A: The Control phase standardizes the improved process through documentation, training, and control plans (often with SPC control charts) to ensure gains are sustained after project closure.

Q: What is transportation as a lean waste?
A: Transportation waste refers to unnecessary movement of materials, products, or information between locations. It adds no value, increases handling costs, and risks damage or delay.

Q: What is waiting as a lean waste?
A: Waiting waste occurs when people, machines, or materials are idle because of delays, imbalances, or poor scheduling. Idle time costs money without producing value for the customer.

Q: What does an np-chart monitor?
A: An np-chart monitors the number of nonconforming (defective) items in samples of constant size. It is appropriate for attribute data where each unit is either pass or fail.

Q: What is a sample size in statistical analysis?
A: Sample size is the number of observations drawn from a population for analysis. Larger samples reduce sampling error and increase statistical power, but require more resources to collect.

Q: What is statistical power in hypothesis testing?
A: Statistical power is the probability of correctly rejecting a false null hypothesis (1 − β). Higher power reduces Type II risk and typically requires larger sample sizes.

Q: What is an I-MR chart used for?
A: An Individuals and Moving Range chart monitors individual measurements and their variability when subgroup sizes are one. It is useful for continuous data where rational subgroups cannot be formed.

Q: What is the Western Electric rules used for?
A: Western Electric rules are sensitivity rules applied to control charts to detect non-random patterns (e.g., 8 points on one side of the centerline) indicating special-cause variation.

Q: What is the purpose of a 5 Whys analysis?
A: The 5 Whys is a root-cause technique that repeatedly asks 'why' (typically five times) to move from a problem's symptoms to its underlying cause. It is simple and best for linear issues.

Q: What is inventory as a lean waste?
A: Inventory waste is excess raw materials, work-in-process, or finished goods beyond immediate need. It ties up capital, occupies space, and can mask underlying process problems.

Q: What is motion as a lean waste?
A: Motion waste refers to unnecessary movement of people (or equipment) such as walking, reaching, or bending. It differs from transportation waste, which involves moving materials or items.

Q: What is over-processing as a lean waste?
A: Over-processing waste occurs when work is done to a higher precision or quality than the customer requires, or when unnecessary steps are added beyond what adds value.

Q: What is defects as a lean waste?
A: Defects waste involves producing items that must be repaired, reworked, scrapped, or replaced. Inspection, rework time, and warranty costs all contribute to this costly form of muda.

Q: What is skills utilization as a lean waste?
A: Skills utilization waste (the eighth muda) occurs when organizations underuse employee talents, knowledge, and creativity—failing to listen, train, or engage workers in improvement.

Q: What is a run chart vs. a control chart?
A: A run chart plots data over time with a median line to detect trends. A control chart adds statistically derived upper and lower control limits (typically ±3σ) to distinguish common from special cause.

Q: What is the Six Sigma Green Belt certification scope?
A: Green Belt certification covers DMAIC methodology, basic statistics, control charts, and project participation. Green Belts lead small projects and assist Black Belts on larger initiatives.

Q: What is the Six Sigma Black Belt certification scope?
A: Black Belt certification requires mastery of advanced statistics, DOE, regression, hypothesis testing, and full DMAIC leadership. Candidates must complete a project with documented financial results.

Q: What is a stakeholder analysis in the Define phase?
A: Stakeholder analysis identifies all parties affected by the project, their interests, influence, and communication needs. It ensures engagement and prevents resistance during execution.

Q: What is a project charter?
A: A project charter is a document created in the Define phase that defines the problem, goal, scope, timeline, team, and metrics for a Six Sigma project. It authorizes the team's work.

Q: What is the cost of poor quality (COPQ)?
A: COPQ is the total cost of activities that would disappear if quality were perfect: scrap, rework, warranty claims, inspections, and lost customer goodwill. Reducing it is a key project metric.

Q: What is a value stream map?
A: A value stream map is a Lean tool that diagrams every step of a process from supplier to customer, distinguishing value-added from non-value-added time to identify improvement opportunities.

Q: What is takt time?
A: Takt time = Available Production Time / Customer Demand. It sets the pace at which a process must produce to meet demand and is the foundation for balancing a production line.

Q: What is cycle time vs. lead time?
A: Cycle time is the time to complete one unit from start to finish. Lead time is the total time from customer order to delivery, including wait, queue, and processing times.

Q: What is standard work in Lean?
A: Standard work documents the current best-known, safest, highest-quality method to perform a task. It serves as a baseline for kaizen and ensures consistency before improvement.

Q: What is a kaizen event?
A: A kaizen event is a short, focused improvement workshop (typically 3–5 days) where a cross-functional team implements rapid changes to a targeted process, then standardizes the new method.

Q: What is a Taguchi loss function?
A: Taguchi's loss function quantifies quality loss as a quadratic function of deviation from target. It argues that any deviation—even within spec—creates cost to society and customer.

Q: What is benchmarking in Six Sigma?
A: Benchmarking compares a process's performance against internal best-in-class units, competitors, or industry leaders to set realistic improvement targets and identify best practices.

Q: What is a brainstorming session used for?
A: Brainstorming generates a large quantity of potential causes, solutions, or ideas without judgment. It is widely used in Analyze and Improve phases, often paired with affinity diagrams or multi-voting.

Q: What is an affinity diagram?
A: An affinity diagram organizes large numbers of brainstormed ideas into natural groupings or themes. It helps teams identify root causes or solution categories when issues seem overwhelming.

Q: What is a matrix diagram in quality tools?
A: A matrix diagram shows the relationship strength between two or more sets of items (e.g., customer requirements and process steps). It helps prioritize where efforts and resources should focus.

Q: What is a force field analysis?
A: Force field analysis lists driving forces for and restraining forces against a proposed change. It is used to plan change management by strengthening drivers and reducing barriers before action.

Q: What is the difference between a continuous and attribute measurement?
A: Continuous measurements yield variable data on a scale (e.g., weight, temperature). Attribute measurements yield discrete pass/fail or count data. Different statistical tools apply to each type.

Q: What is the standard deviation's role in calculating sigma level?
A: Sigma level measures how many standard deviations fit between the process mean and the nearest specification limit. A 6-sigma process allows 3.4 defects per million opportunities, indicating extremely low variability relative to specification width.

Q: Define the term 'rolled throughput yield' calculation basis.
A: RTY is calculated by multiplying the first-pass yield of each sequential process step. For example, if three steps each have 95% yield, RTY = 0.95 × 0.95 × 0.95 = 0.857 or 85.7%, revealing hidden losses.

Q: What is a sampling plan's acceptance number in acceptance sampling?
A: The acceptance number is the maximum number of defects allowed in a sample for the lot to be accepted. It is determined by the AQL (acceptable quality level) and LTPD (lot tolerance percent defective) chosen for the sampling plan.

Q: What is the difference between attribute and variable data?
A: Attribute data is categorical—pass/fail, go/no-go counts of defects. Variable data is measured on a continuous scale like temperature, weight, or length. Variable data provides more statistical power with smaller sample sizes.

Q: What does a Box-Cox transformation accomplish?
A: Box-Cox transformation mathematically transforms non-normal data into an approximately normal distribution using a power parameter lambda. This enables valid use of control charts and capability indices requiring normality.

Q: What is the purpose of a cause-and-effect matrix in six sigma?
A: The cause-and-effect matrix (C&E matrix) prioritizes process inputs by correlating them to customer-critical outputs (CTQs). Inputs with high correlation scores become focus areas for data collection and improvement efforts.

Q: What is a Type II error in hypothesis testing?
A: A Type II error (beta) occurs when failing to reject a false null hypothesis. It represents missing a real effect. Statistical power (1-β) is the probability of correctly rejecting a false null hypothesis.

Q: What is a benchmark sigma for world-class performance?
A: World-class organizations typically operate at 5-sigma or higher, equating to 233 or fewer defects per million opportunities. Six sigma (3.4 DPMO) represents the gold standard quality goal.

Q: What is the purpose of stratification in data analysis?
A: Stratification separates data into subgroups (by shift, machine, operator, material) to reveal patterns hidden in aggregated data. It helps identify special causes of variation and sources of defects.

Q: What is a defect opportunity in six sigma?
A: A defect opportunity is any instance where a unit could fail to meet a customer requirement. For a bill, opportunities might include correct name, amount, address, and date—each counted separately for DPMO calculation.

Q: What is the difference between nominal and tolerance in specifications?
A: Nominal is the target or ideal value of a specification. Tolerance is the allowable deviation from nominal, expressed as a range (e.g., 10mm ± 0.1mm) or as upper/lower specification limits.

Q: What is an OC curve in acceptance sampling?
A: An Operating Characteristic (OC) curve plots the probability of accepting a lot against the true fraction defective. It shows the sampling plan's discriminating power between good and bad lots at various quality levels.

Q: What is a chi-square test used for in six sigma?
A: Chi-square tests analyze categorical data to determine if observed frequencies differ significantly from expected frequencies. Common uses include testing independence in contingency tables and goodness-of-fit assessments.

Q: What is the difference between LSL and USL?
A: LSL (Lower Specification Limit) is the minimum acceptable value; USL (Upper Specification Limit) is the maximum acceptable value. Both define the customer's tolerance range; values outside indicate defects.

Q: What is the empirical rule (68-95-99.7) for normal distributions?
A: Approximately 68% of data falls within ±1 sigma, 95% within ±2 sigma, and 99.7% within ±3 sigma of the mean. This rule underlies control chart limits and process capability calculations assuming normality.

Q: What is a discrete event simulation in six sigma?
A: Discrete event simulation models process flows over time, capturing variability in arrival rates, processing times, and resources. It predicts bottlenecks, cycle times, and throughput before implementing physical changes.

Q: What is the difference between long-term and short-term capability studies?
A: Short-term capability (Pp, Ppk) uses data from a stable, controlled period reflecting inherent process variation. Long-term capability (Cp, Cpk) includes all sources of variation over time, typically showing wider spread.

Q: What is a force field analysis used for?
A: Force field analysis identifies driving forces supporting change and restraining forces opposing it. Leaders can then strengthen drivers and weaken restraints to facilitate successful implementation of improvements.

Q: What is the control phase's documentation deliverable?
A: The control plan documents the updated process, including control points, responsible owners, reaction plans for out-of-control conditions, training requirements, and metrics for ongoing monitoring and sustainment.

Q: What is a fractional factorial design?
A: A fractional factorial design tests only a subset of full factorial runs using confounding principles. For example, a 2^(5-1) design runs 16 trials instead of 32, saving resources while identifying main effects efficiently.

Q: What is a Gantt chart used for in project management?
A: A Gantt chart visually displays project tasks along a timeline, showing start/end dates, durations, dependencies, and milestones. Six sigma black belts use it to track DMAIC phases and ensure timely completion.

Q: What is the purpose of a Pareto chart?
A: A Pareto chart combines a bar graph (descending frequencies) with a cumulative percentage line. It applies the 80/20 principle—showing which vital few categories cause most problems, guiding prioritization of improvement efforts.

Q: What is the difference between noise and signal factors in DOE?
A: Signal factors are controllable inputs that affect the response in desirable ways. Noise factors are uncontrollable variables (humidity, raw material variation) that the design should make robust against for consistent performance.

Q: What is an Affinity diagram used for?
A: An Affinity diagram organizes large numbers of ideas into natural groupings based on relationships. It synthesizes brainstorming output and qualitative data into themes, often used during VOC analysis and problem definition.

Q: What is MSA in measurement system analysis?
A: MSA evaluates the measurement system's accuracy, precision, stability, and linearity using tools like Gage R&R. A capable measurement system has total variation less than 10% of process tolerance for reliable decisions.

Q: What is a Brainstorming rule in six sigma teams?
A: Brainstorming rules: defer judgment, encourage wild ideas, build on others' suggestions, stay focused on topic, and aim for quantity. After generation, ideas are evaluated using criteria like feasibility and impact.

Q: What is the normal distribution's probability density function?
A: f(x) = (1/(σ√(2π))) × e^(-((x-μ)²/(2σ²))). The bell curve is symmetric around mean μ, with spread determined by standard deviation σ. Approximately 50% of area lies within ±0.6745σ of the mean.

Q: What is a cost-benefit analysis in the improve phase?
A: Cost-benefit analysis quantifies expected savings (defect reduction, cycle time improvement) versus implementation costs (training, equipment, software). A positive ROI justifies proceeding with the selected solution.

Q: What is a Tree Diagram used for?
A: A tree diagram systematically breaks down a broad goal into smaller, detailed tasks or sub-problems. It's used to develop CTQ trees, work breakdown structures, and decision trees for complex problems.

Q: What is the difference between continuous and discrete data?
A: Continuous data can take any value within a range (length, temperature). Discrete data has countable values (defects per unit, number of complaints). Continuous data provides more information but requires different statistical tools.

Q: What is the Define phase's primary deliverable?
A: The Define phase delivers the project charter, including problem statement, goal, scope, timeline, team members, and business case. It also includes the SIPOC diagram and VOC translation into CTQs.

Q: What is a matrix diagram used for?
A: A matrix diagram shows the relationship strength between two or more sets of items using symbols or numbers. Types include L-shaped, T-shaped, Y-shaped, and roof-shaped matrices for various relationship analyses.

Q: What is process mapping versus value stream mapping?
A: Process mapping details individual task steps in a workflow. Value stream mapping captures the entire production flow including material and information flows, cycle times, wait times, and inventory levels to identify waste.

Q: What is a Benchmarking study in six sigma?
A: Benchmarking compares processes, performance metrics, or practices against industry best-in-class organizations. It establishes realistic improvement targets and identifies best practices to adapt for competitive advantage.

Q: What is a Poka-Yoke device?
A: Poka-Yoke (mistake-proofing) is a device or procedure that prevents or detects errors before they become defects. Examples include USB connectors that fit only one way and ATM card slots that retain cards during transactions.

Q: What is a Pilot study's purpose before full implementation?
A: A pilot study tests the proposed solution on a small scale to verify effectiveness, identify unforeseen issues, refine procedures, and build evidence. Successful pilots justify broader rollout and resource commitment.

Q: What is the Analyze phase's key question?
A: The Analyze phase asks: 'What are the vital few root causes of the problem?' It uses statistical tools like hypothesis tests, regression, and DOE to verify potential causes identified during brainstorming.

Q: What is Lean Six Sigma's primary value proposition?
A: Lean Six Sigma combines Lean's waste elimination with Six Sigma's variation reduction. It delivers faster cycle times, lower costs, and higher quality by addressing both process efficiency and statistical control simultaneously.

Q: What is Standardization in the control phase?
A: Standardization updates standard operating procedures, work instructions, and training materials to reflect the improved process. It ensures consistent execution, prevents regression, and institutionalizes the gains across the organization.

Q: What is the typical role of a Yellow Belt in Six Sigma?
A: Yellow Belts are subject-matter experts who participate part-time on projects led by Green or Black Belts. They support data collection, basic analysis, and help implement improvements within their own work areas.

Q: What does a u-chart monitor in quality control?
A: A u-chart plots the number of defects per unit when sample sizes vary. It is used when the opportunity for defects differs across observations, unlike a c-chart which assumes constant sample size.

Q: What is the difference between an attribute chart and a variable chart?
A: Attribute charts (p, np, c, u) track discrete data such as pass/fail or defect counts. Variable charts (X-bar, R, S, I-MR) track continuous measurements like length, weight, or temperature.

Q: What is the DMAIC Improve phase objective?
A: The Improve phase develops, pilots, and implements solutions that address root causes identified during Analyze. It focuses on generating alternatives, selecting the best option, and validating gains statistically.

Q: What is a Gantt chart used for in a Six Sigma project?
A: A Gantt chart displays the project schedule as horizontal bars across a timeline, showing task durations, dependencies, milestones, and resource assignments for tracking DMAIC execution.

Q: What is the goal of the Analyze phase in DMAIC?
A: Analyze identifies root causes of defects and validates them with data. It uses tools like regression, ANOVA, hypothesis testing, Pareto, and fishbone diagrams to confirm cause-and-effect relationships.

Q: What is a cause-and-effect matrix also called a CE matrix?
A: It is a prioritization tool that links customer requirements (Y) to process inputs (X) by scoring relationships and assigning weights, helping teams focus improvement efforts on the most critical inputs.

Q: What does a Box-Cox transformation do?
A: Box-Cox mathematically transforms non-normal data into an approximately normal distribution, allowing control charts and capability indices that assume normality to be applied reliably.

Q: What is the difference between short-term and long-term capability studies?
A: Short-term capability (Cp, Cpk) uses data collected under controlled conditions reflecting only common-cause variation. Long-term capability (Pp, Ppk) uses data spanning a longer period including routine variation.

Q: What is a Z-score in Six Sigma?
A: A Z-score expresses how many standard deviations a data point lies from the mean. Higher Z-scores indicate better process performance; Six Sigma quality corresponds to a Z of 6.

Q: What is the difference between Pp and Ppk?
A: Pp measures overall process spread relative to specification width; Ppk centers the spread using the actual process mean. Both use sample standard deviation, unlike Cp/Cpk which use within-subgroup variation.

Q: What is a Lean value stream?
A: A value stream is the complete set of activities required to deliver a product or service from raw materials to the customer, including both value-added and non-value-added steps.

Q: What is the formula for Z-score standard normal?
A: Z = (X - mean) / standard deviation. It standardizes values to a normal distribution with mean 0 and standard deviation 1 for comparison and probability lookup.

Q: What does a Boxplot reveal about a dataset?
A: A boxplot displays the median, quartiles, and outliers. It quickly shows data spread, skewness, and identifies unusual observations for further investigation during Analyze phase.

Q: What is a benchmark in Six Sigma projects?
A: A benchmark is a reference standard or best practice from inside or outside the organization used to compare process performance and identify improvement targets.

Q: What is the difference between a continuous and discrete variable?
A: Continuous variables can take any value within a range (e.g., weight, time). Discrete variables are countable categories or counts (e.g., defects, color codes).

Q: What is a sampling plan?
A: A sampling plan defines how many units to inspect, how often, and by what method. It balances inspection cost against risk of accepting defective product or rejecting good product.

Q: What is the purpose of a run test on a control chart?
A: Run tests detect non-random patterns such as trends, shifts, or cycles that indicate special-cause variation even when points remain within control limits.

Q: What is NDC in Gage R&R?
A: NDC (Number of Distinct Categories) indicates the count of non-overlapping confidence intervals the measurement system can distinguish. Industry guidance typically requires NDC of at least 5.

Q: What is the difference between special and common cause in Six Sigma?
A: Special cause variation is non-random and assignable to a specific event. Common cause variation is inherent to the process and predictable. Only special causes should trigger process stop-and-investigate.

Q: What is a Confidence Level in hypothesis testing?
A: The confidence level is 1 minus alpha, expressing the probability that the test correctly rejects a false null hypothesis. Common levels are 90%, 95%, and 99%.

Q: What is a one-tailed vs two-tailed hypothesis test?
A: A one-tailed test detects an effect in one direction (greater than or less than). A two-tailed test detects any difference, regardless of direction, and splits alpha across both tails.

Q: What is replication in Design of Experiments?
A: Replication is repetition of experimental runs under identical conditions to estimate experimental error and increase the power to detect factor effects statistically.

Q: What is blocking in DOE?
A: Blocking groups similar experimental units together to reduce nuisance variability. It improves precision by accounting for differences that are not the primary factors of interest.

Q: What is interaction between factors in DOE?
A: An interaction occurs when the effect of one factor on the response depends on the level of another factor. Detecting interactions is a key DOE objective.

Q: What is the purpose of randomization in experiments?
A: Randomization allocates treatments to experimental units to reduce bias from uncontrolled factors, ensuring statistical independence and validity of inference.

Q: What is a confounding factor in DOE?
A: A confounding factor is a variable whose effect on the response cannot be separated from the effect of another factor, making it impossible to attribute observed changes to a single cause.

Q: What is a Response Surface Methodology?
A: RSM is a set of DOE techniques that model the relationship between factors and a response using second-order designs, enabling optimization rather than just factor screening.

Q: What is the difference between nominal and ordinal data?
A: Nominal data are categories without order (e.g., red/blue/green). Ordinal data are ranked categories (e.g., low/medium/high) but intervals between ranks may not be equal.

Q: What is the purpose of a stratified sample?
A: Stratified sampling divides a heterogeneous population into homogeneous subgroups (strata) and randomly samples within each, ensuring representation and reducing sampling error.

Q: What is a Standard Operating Procedure?
A: An SOP is a documented step-by-step set of instructions for routine tasks. SOPs are common outputs of the Control phase to sustain improvements and standardize new processes.

Q: What is a control plan in Six Sigma?
A: A control plan lists the critical process inputs, monitoring methods, reaction plans, and responsible owners for each CTQ to sustain improvements after project closure.

Q: What is an Operating Characteristic curve used for?
A: An OC curve shows the probability of accepting a lot versus its true quality level. It helps select sample sizes and acceptance criteria balancing producer and consumer risk.

Q: What is Producer's Risk and Consumer's Risk?
A: Producer's Risk is the probability of rejecting a good lot (alpha). Consumer's Risk is the probability of accepting a bad lot (beta). Both must be controlled when designing sampling plans.

Q: What is a critical to quality tree (CTQ)?
A: A CTQ tree translates broad VOC needs into measurable requirements through layers: customer needs, CTQs, and measurable specifications with units, tolerances, and operational definitions.

Q: What is a Pareto principle in Six Sigma?
A: The Pareto principle states roughly 80% of problems come from 20% of causes. A Pareto chart ranks defect categories by frequency, guiding teams to focus on the vital few causes.

Q: What is a key process input variable (KPIV)?
A: A KPIV is an upstream process input that significantly influences a CTQ output (KPOV). Identifying KPIVs through cause-and-effect analysis helps target improvement efforts.

Q: What is the Define phase's primary deliverable in a DMAIC project?
A: A completed project charter that clearly defines the problem statement, scope, goals, timeline, team members, and stakeholders, formally authorizing the project.

Q: What does the Measure phase primarily establish in DMAIC?
A: A reliable baseline of the current process performance by collecting data, identifying CTQs, and validating the measurement system (Gage R&R) before improvements.

Q: What is the main purpose of the Analyze phase in DMAIC?
A: To identify and verify the root causes of defects or variation by using statistical tools such as regression, ANOVA, hypothesis testing, and Pareto analysis.

Q: What is the typical improvement focus of the Improve phase?
A: Developing, piloting, and implementing solutions that eliminate root causes, reduce defects, and improve process capability (Cp, Cpk) to meet project goals.

Q: What is the goal of the Control phase in DMAIC?
A: To sustain improvements by updating process documentation, implementing control plans, control charts, and training so gains do not regress over time.

Q: What is a Yellow Belt in Six Sigma?
A: An employee with basic Six Sigma awareness who supports projects part-time, participates in problem-solving, and helps local improvements but does not lead teams.

Q: What does a Green Belt typically lead?
A: Smaller, department-level improvement projects part-time while maintaining regular duties, applying DMAIC tools under the guidance of a Black Belt or Master Black Belt.

Q: What statistical tool is used to compare means of three or more groups?
A: ANOVA (Analysis of Variance), which tests whether at least one group mean differs significantly by analyzing variance between and within groups.

Q: What does a u-chart monitor in statistical process control?
A: The number of defects per unit across varying sample sizes, making it suitable for processes where the inspection area or opportunity changes between samples.

Q: What does a Cp value of 1.33 generally indicate?
A: A capable process where the total process spread fits within the specification limits with some buffer; 1.67 is often targeted for critical Six Sigma processes.

Q: What is a sigma shift used in Six Sigma calculations?
A: A 1.5 standard deviation shift of the process mean over the long term, accounting for real-world drift and yielding a 3.4 DPMO at six sigma performance.

Q: What does a Box-and-Whisker plot display?
A: The five-number summary (minimum, Q1, median, Q3, maximum) and potential outliers, useful for comparing distribution spread and skewness across groups.

Q: What does the term 'kaizen' mean in lean?
A: A Japanese word meaning continuous, incremental improvement involving all employees, often through small, frequent changes rather than large innovations.

Q: What is the difference between poka-yoke and 5S?
A: Poka-yoke is mistake-proofing a process to prevent errors; 5S (Sort, Set, Shine, Standardize, Sustain) is a workplace organization methodology for efficiency.

Q: What is a benchmark in Six Sigma project selection?
A: A reference point—internal, competitive, or industry best—used to set realistic improvement goals and justify project scope.

Q: What is the standard normal distribution's mean and standard deviation?
A: A mean of 0 and standard deviation of 1, serving as the reference for calculating Z-scores and probability values in capability studies.

Q: What is a Z-score in process capability analysis?
A: The number of standard deviations a data point lies from the mean, used to determine how many specification limits are within the process spread.

Q: What is the formula for process yield in Six Sigma?
A: Yield = (Good Units Produced) ÷ (Total Units Started), often expressed as a percentage to track First Pass Yield or Rolled Throughput Yield.

Q: What does a control chart's Lower Control Limit (LCL) typically represent?
A: Three standard deviations below the process mean, the boundary below which a plotted point signals special cause variation requiring investigation.

Q: What is the purpose of a Pilot Study in the Improve phase?
A: To test proposed solutions on a small scale before full implementation, validating effectiveness, identifying issues, and refining the change before rollout.

Q: What is a Standard Operating Procedure (SOP) used for in Control?
A: Documenting the improved, standardized work instructions so operators consistently perform the new process and improvements are sustained long-term.

Q: What is the 80/20 rule as applied in Six Sigma?
A: The Pareto principle stating roughly 80% of problems come from 20% of causes, guiding teams to focus on the vital few issues for greatest impact.

Q: What is the difference between Common Cause and Special Cause on a control chart?
A: Common cause is inherent, random process variation; special cause is an external, assignable factor producing non-random patterns that must be investigated.

Q: What does a non-normal distribution imply for capability analysis?
A: Standard Cp/Cpk formulas may be invalid; teams should transform data or use non-normal capability indices (e.g., Cp_alt) to assess true capability.

Q: What is a Cause-and-Effect Matrix used for?
A: Prioritizing potential process inputs (Xs) by their relationship strength to customer outputs (Ys), guiding data collection toward vital few causes.

Q: What is the difference between a one-tailed and two-tailed hypothesis test?
A: A one-tailed test checks for an effect in one direction; a two-tailed test checks for an effect in either direction, affecting the critical region placement.

Q: What is a confidence level commonly used in Six Sigma hypothesis testing?
A: 95% confidence (alpha = 0.05) is standard, meaning there is a 5% risk of rejecting the null hypothesis when it is actually true (Type I error).

Q: What is the formula for sample standard deviation?
A: s = sqrt(Σ(xi – x̄)² ÷ (n – 1)), using n–1 (Bessel's correction) to provide an unbiased estimator of population standard deviation.

Q: What is Multi-Vari analysis used for in Six Sigma?
A: A graphical tool that displays variation across positional, cyclical, and within-piece categories to help identify which sources contribute most to variation.

Q: What is the difference between CTQ and KPI?
A: CTQ (Critical to Quality) is a customer-driven requirement; KPI (Key Performance Indicator) is a metric tracking overall business or process performance.

Q: What is a 5S audit used for in lean?
A: Periodically evaluating workplace organization against Sort, Set, Shine, Standardize, and Sustain standards to maintain discipline and identify improvement opportunities.

Q: What is the difference between Push and Pull production systems?
A: Push produces based on forecasted demand, often creating inventory; Pull produces based on actual downstream consumption, reducing waste and lead time.

Q: What is the role of a Sponsor in a Six Sigma project?
A: A senior leader who champions the project, removes organizational barriers, secures resources, and ensures alignment with strategic business objectives.

Q: What is a Tollgate Review in DMAIC?
A: A formal phase-end review where leadership evaluates deliverables, validates progress, and authorizes the team to proceed to the next DMAIC phase.

Q: What is the difference between an RSM and a Full Factorial DOE?
A: Response Surface Methodology explores curvature with fewer runs in a designed region; Full Factorial evaluates all factor combinations at every level exhaustively.

Q: What is the difference between population and sample in statistics?
A: A population includes all items of interest; a sample is a subset drawn from the population used to estimate population parameters due to practical constraints.

Q: What is the Measure phase's key objective?
A: To quantify the problem by collecting baseline data, establishing reliable measurement systems, and determining the current process performance using capability indices and defect metrics.

Q: What does MSA stand for in Six Sigma?
A: Measurement System Analysis. It evaluates the gauge, appraiser, and method variability to confirm data integrity before drawing statistical conclusions.

Q: What is the Analyze phase's main goal?
A: To identify the root causes of defects and variation by applying statistical tools such as hypothesis tests, regression, ANOVA, and Pareto analysis.

Q: What is the Improve phase's purpose?
A: To develop, pilot, and implement solutions that eliminate root causes, optimize process inputs, and validate improvement using DOE and pilot data.

Q: What is the Control phase's outcome?
A: Standardized processes with documentation, updated SOPs, control plans, training, and monitoring systems like SPC charts to sustain gains.

Q: What does DPMO stand for and what does it measure?
A: Defects Per Million Opportunities. It quantifies process performance by counting defects normalized to one million possible opportunities regardless of product complexity.

Q: What is a Pareto chart based on?
A: The 80/20 principle. It ranks defect causes or problem categories by frequency or cost, helping teams prioritize the vital few over the trivial many.

Q: What is the difference between continuous and attribute data?
A: Continuous data are measurable on a scale (length, weight, time). Attribute data are categorical, counting defects or pass/fail outcomes.

Q: What is an I-MR chart used to monitor?
A: Individual values and Moving Range. It is ideal for small sample sizes where subgrouping is impractical, plotting each observation and its consecutive variation.

Q: What are Western Electric Rules?
A: A set of sensitivity tests detecting non-random patterns on control charts, such as seven points in a row on one side of the mean.

Q: What is Rolled Throughput Yield (RTY)?
A: The product of yields across all process steps. It captures the probability that a single unit passes every step defect-free from start to end.

Q: What is Process Sigma level?
A: A statistical measure of process capability indicating how many standard deviations fit between the process mean and the nearest specification limit.

Q: What is the target Defect Rate for Six Sigma?
A: 3.4 defects per million opportunities (DPMO), corresponding to 4.5 sigma long-term performance with a 1.5 sigma shift allowance.

Q: What is a Green Belt's role?
A: A part-time Six Sigma practitioner who leads smaller projects, supports Black Belt initiatives, and applies basic tools within their functional area.

Q: What does a Black Belt typically do?
A: Leads full-time DMAIC projects, applies advanced statistical methods, mentors teams, and drives measurable financial savings for the organization.

Q: What is the Kano model used for?
A: Categorizing customer requirements into must-be, one-dimensional, and delighters to prioritize features that drive satisfaction and competitive advantage.

Q: What is the Voice of the Customer (VOC)?
A: A structured process of capturing customer expectations, preferences, and complaints through interviews, surveys, focus groups, and market research.

Q: What does an S-chart monitor?
A: The standard deviation within each subgroup, used when subgroup sizes exceed ten observations where the range becomes an inefficient estimator.

Q: What does a u-chart monitor?
A: The number of defects per unit when subgroup sizes vary, normalizing count data across differing opportunity windows.

Q: What is statistical power?
A: The probability of correctly rejecting a false null hypothesis (1 minus beta), reflecting the test's ability to detect real effects.

Q: What is a confidence interval?
A: A range estimate for a population parameter derived from sample data, expressing uncertainty with a stated probability level such as 95%.

Q: What is the formula for Process Capability Index Cp?
A: Cp = (USL − LSL) ÷ (6σ), comparing specification width to natural process spread assuming perfect centering on the midpoint.

Q: What is the formula for Cpk?
A: Cpk = Min[(USL − μ)/3σ, (μ − LSL)/3σ], measuring capability relative to the nearest specification limit while accounting for centering.