Six Sigma | Control Phase & SPC Tools | 100+ MCQ with Answers
Q1. In the Improve phase, “Measure II” primarily refers to which activity?
A. Baseline data collection
B. Post-implementation validation of improvements
C. Root cause analysis
D. Project charter creation
✅ Answer: B. Post-implementation validation of improvements
Q2. The main goal of the Improve phase in a Six Sigma project is to:
A. Collect more defects
B. Eliminate root causes and validate improvements
C. Freeze process changes
D. Conduct capability analysis
✅ Answer: B. Eliminate root causes and validate improvements
Q3. In the Malgudi Hospital case, post-improvement data was collected for how many samples?
A. 7 samples
B. 24 samples
C. 48 samples
D. 100 samples
✅ Answer: C. 48 samples
Q4. What is the key objective when comparing baseline and post-improvement data?
A. Increase standard deviation
B. Reduce average time and variation
C. Maintain existing process mean
D. Increase the number of defects
✅ Answer: B. Reduce average time and variation
Q5. Before recalculating capability metrics, the process must be checked for:
A. Efficiency
B. Stability
C. Profitability
D. Throughput
✅ Answer: B. Stability
Q6. Which chart pair is typically used to assess process stability for continuous data?
A. P and NP charts
B. $\bar{X}$ and R charts
C. U and C charts
D. Pareto and Run charts
✅ Answer: B. $\bar{X}$ and R charts
Q7. In an in-control process, all sample points lie within:
A. ±6σ
B. ±2σ
C. ±3σ control limits
D. ±1σ control limits
✅ Answer: C. ±3σ control limits
Q8. If assignable causes are detected in control charts, the next step is to:
A. Ignore the data point
B. Remove and investigate the cause
C. Recalculate limits immediately
D. Reduce sample size
✅ Answer: B. Remove and investigate the cause
Q9. The formula for process capability ($C_p$) is:
A. $(USL - LSL)/3σ$
B. $(USL - LSL)/6σ$
C. $(USL + LSL)/6σ$
D. $(USL/LSL) * σ$
✅ Answer: B. $(USL - LSL)/6σ$
Q10. A $C_p$ value of 0.757 indicates a process performing between which sigma levels?
A. 1–2 sigma
B. 2–3 sigma
C. 3–4 sigma
D. 4–5 sigma
✅ Answer: B. 2–3 sigma
Q11. The $C_{pk}$ value is used to check:
A. Process spread
B. Process centering
C. Process cost
D. Measurement frequency
✅ Answer: B. Process centering
Q12. In the Malgudi case, the post-improvement mean registration time was approximately:
A. 179 seconds
B. 120 seconds
C. 89 seconds
D. 60 seconds
✅ Answer: C. 89 seconds
Q13. The ideal process center for a tolerance of 0–120 seconds is:
A. 179 seconds
B. 89 seconds
C. 60 seconds
D. 30 seconds
✅ Answer: C. 60 seconds
Q14. Defect rate in Six Sigma is measured in:
A. DPU
B. DPMO
C. ROI
D. COPQ
✅ Answer: B. DPMO
Q15. What was the calculated DPMO for Malgudi Hospital post-improvement?
A. 1,200
B. 12,240
C. 120,000
D. 240,000
✅ Answer: B. 12,240
Q16. In Six Sigma, the Z-score represents:
A. Cost of defects
B. Process centering value
C. Standardized distance from the mean
D. Data collection frequency
✅ Answer: C. Standardized distance from the mean
Q17. The null hypothesis ($H_0$) in the Malgudi validation test stated that:
A. The project improved performance
B. The project had no impact
C. The mean time decreased
D. The defect rate dropped
✅ Answer: B. The project had no impact
Q18. A low P-value in hypothesis testing indicates:
A. No significant difference
B. Significant improvement
C. Poor data quality
D. Need for larger samples
✅ Answer: B. Significant improvement
Q19. The final phase of the DMAIC cycle is:
A. Analyze
B. Control
C. Measure
D. Improve
✅ Answer: B. Control
Q20. The purpose of the Control phase is to:
A. Identify root causes
B. Sustain improvement
C. Validate baseline data
D. Recalculate sigma levels
✅ Answer: B. Sustain improvement
Q21. The primary deliverable of the Control phase is:
A. Process Charter
B. Control Plan
C. Capability Chart
D. Pareto Analysis
✅ Answer: B. Control Plan
Q22. The Control Plan contains all of the following except:
A. Monitoring methods
B. Escalation plan
C. Control chart limits
D. Project funding details
✅ Answer: D. Project funding details
Q23. A Control Plan’s “Reaction Plan” defines:
A. How to collect data
B. What to do if something goes wrong
C. Who will manage the project
D. Frequency of training
✅ Answer: B. What to do if something goes wrong
Q24. Which phase ensures people follow new SOPs consistently?
A. Define
B. Analyze
C. Control
D. Measure
✅ Answer: C. Control
Q25. Control charts are a part of which broader methodology?
A. Benchmarking
B. SPC (Statistical Process Control)
C. Cost-Benefit Analysis
D. Value Stream Mapping
✅ Answer: B. SPC (Statistical Process Control)
Q26. The main purpose of Control Charts is to:
A. Identify outliers
B. Detect assignable causes of variation
C. Measure process speed
D. Reduce mean shift
✅ Answer: B. Detect assignable causes of variation
Q27. If a point lies outside ±3σ limits, it indicates:
A. Natural variation
B. Assignable cause
C. Normal process behavior
D. Sampling error
✅ Answer: B. Assignable cause
Q28. Post-project, a shift in process average toward improvement is best shown using:
A. Histogram
B. Control Chart
C. Scatter Plot
D. Pareto Chart
✅ Answer: B. Control Chart
Q29. For variable data with sample size between 2 and 9, which chart pair is used?
A. $\bar{X}$ and R Chart
B. $\bar{X}$ and S Chart
C. NP Chart
D. P Chart
✅ Answer: A. $\bar{X}$ and R Chart
Q30. When sample size ≥ 10, the correct control chart pair is:
A. $\bar{X}$ and R Chart
B. $\bar{X}$ and S Chart
C. XMR Chart
D. C Chart
✅ Answer: B. $\bar{X}$ and S Chart
Q31. For $n=1$ (individual readings), the suitable chart is:
A. P Chart
B. IMR (XMR) Chart
C. S Chart
D. NP Chart
✅ Answer: B. IMR (XMR) Chart
Q32. XMR charts are often used in:
A. Attribute defect tracking
B. Continuous sequential data monitoring
C. Customer satisfaction analysis
D. Stratification studies
✅ Answer: B. Continuous sequential data monitoring
Q33. In destructive testing, the best control chart to use is:
A. P Chart
B. XMR Chart
C. R Chart
D. C Chart
✅ Answer: B. XMR Chart
Q34. Which control chart tracks number of defects per unit when sample size varies?
A. P Chart
B. NP Chart
C. U Chart
D. C Chart
✅ Answer: C. U Chart
Q35. The C Chart is used when:
A. Sample size changes
B. Sample size is constant
C. Process is non-normal
D. There are multiple outputs
✅ Answer: B. Sample size is constant
Q36. Attribute data measuring proportion of defective items with variable $n$ uses:
A. NP Chart
B. P Chart
C. C Chart
D. R Chart
✅ Answer: B. P Chart
Q37. Attribute data tracking number of defective items with constant $n$ uses:
A. U Chart
B. NP Chart
C. S Chart
D. XMR Chart
✅ Answer: B. NP Chart
Q38. The Control phase ensures the process does not:
A. Continue improving
B. Revert to old habits
C. Reduce variation
D. Increase defect count
✅ Answer: B. Revert to old habits
Q39. Which of these is not typically part of a control plan?
A. SOP updates
B. Reaction plans
C. Marketing strategy
D. Audit schedules
✅ Answer: C. Marketing strategy
Q40. The Control Plan identifies which factors?
A. Critical input and output parameters
B. Customer demographics
C. Employee turnover
D. Inventory details
✅ Answer: A. Critical input and output parameters
Q41. Project closure includes documenting:
A. Root cause analysis
B. Lessons learned and benefits
C. Marketing metrics
D. Training logs only
✅ Answer: B. Lessons learned and benefits
Q42. The final process ownership is transferred to:
A. Six Sigma Black Belt
B. Process Owner
C. Project Sponsor
D. Customer
✅ Answer: B. Process Owner
Q43. Control activities and results are detailed in which document?
A. Control Chart
B. Project Closure Document
C. CTQ Diagram
D. Process Charter
✅ Answer: B. Project Closure Document
Q44. Post-project monitoring of results should continue for approximately:
A. 3 months
B. 6 months
C. 1 year
D. 5 years
✅ Answer: C. 1 year
Q45. The analogy “changing the tyre vs. redesigning the wheel” differentiates between:
A. Define and Measure
B. Control and Six Sigma improvement
C. Analyze and Improve
D. VOC and COPQ
✅ Answer: B. Control and Six Sigma improvement
Q46. In the Control vs. Six Sigma analogy, changing a flat tyre represents:
A. Eliminating natural variation
B. Correcting assignable cause
C. Increasing customer value
D. Statistical control
✅ Answer: B. Correcting assignable cause
Q47. Redesigning the wheel material represents:
A. Process reengineering to reduce common causes
B. Routine maintenance
C. Minor corrective action
D. Sample validation
✅ Answer: A. Process reengineering to reduce common causes
Q48. The Control phase primarily focuses on reducing:
A. Common cause variation
B. Assignable cause variation
C. Financial losses
D. Process throughput
✅ Answer: B. Assignable cause variation
Q49. Six Sigma projects focus on reducing:
A. Assignable cause variation
B. Natural (common cause) variation
C. Sampling frequency
D. SOP complexity
✅ Answer: B. Natural (common cause) variation
Q50. Continuous monitoring through SPC ensures:
A. Data redundancy
B. Process stability
C. Decreased output
D. Higher cost
✅ Answer: B. Process stability
Q51. What is the primary purpose of recalculating process capability after improvement?
A. To determine team performance
B. To verify whether the new process meets customer tolerance
C. To measure project ROI
D. To update the SIPOC diagram
✅ Answer: B. To verify whether the new process meets customer tolerance
Q52. A process with $C_p < 1$ indicates that:
A. The process is performing excellently
B. The process variation exceeds the tolerance limits
C. The process is perfectly centered
D. There is no need for improvement
✅ Answer: B. The process variation exceeds the tolerance limits
Q53. If $C_p > C_{pk}$, it means:
A. The process is off-center
B. The process is too narrow
C. The process is ideal
D. The data collection is insufficient
✅ Answer: A. The process is off-center
Q54. A process is said to be “in control” when:
A. Variation is only due to common causes
B. Assignable causes dominate
C. Defects occur unpredictably
D. Standard deviation is undefined
✅ Answer: A. Variation is only due to common causes
Q55. Which of the following tools helps visualize both process average and range stability?
A. Histogram
B. $\bar{X}$ and R Chart
C. Pareto Chart
D. Scatter Diagram
✅ Answer: B. $\bar{X}$ and R Chart
Q56. In SPC, an upward shift in process mean usually signals:
A. Measurement error
B. Assignable cause variation
C. Random noise
D. Poor sampling
✅ Answer: B. Assignable cause variation
Q57. A point outside control limits in a Control Chart implies:
A. The process is under perfect control
B. Special cause variation is likely present
C. Common cause variation is dominant
D. Data was collected incorrectly
✅ Answer: B. Special cause variation is likely present
Q58. The formula $Z = \frac{X - \bar{X}}{\sigma}$ is used to compute:
A. Process capability index
B. Control limit
C. Standardized score
D. Sigma level directly
✅ Answer: C. Standardized score
Q59. If the upper specification limit (USL) is 120 seconds and the mean is 89 seconds, the Z-score helps determine:
A. Defects beyond the upper limit
B. Process centering accuracy
C. Sample mean
D. Process input variability
✅ Answer: A. Defects beyond the upper limit
Q60. A process with 12,240 DPMO can be considered:
A. Unacceptable
B. World-class
C. Reasonably good
D. Below 1-sigma
✅ Answer: C. Reasonably good
Q61. Hypothesis testing in Six Sigma confirms whether:
A. Data collection is correct
B. Improvement is statistically significant
C. Variation is minimal
D. The project meets budget
✅ Answer: B. Improvement is statistically significant
Q62. The p-value in a t-test indicates:
A. The cost per defect
B. The probability that results are due to chance
C. The capability ratio
D. The team’s confidence level
✅ Answer: B. The probability that results are due to chance
Q63. If the p-value < 0.05, what should be concluded?
A. Accept the null hypothesis
B. Reject the null hypothesis
C. Recollect data
D. Increase sample size
✅ Answer: B. Reject the null hypothesis
Q64. In the Control Plan, monitoring frequency should be determined by:
A. Operator preference
B. Criticality of the process
C. Number of employees
D. Cost of raw material
✅ Answer: B. Criticality of the process
Q65. The “Reaction Plan” component of the Control Plan ensures:
A. Corrective actions are predefined for out-of-control conditions
B. Financial reporting accuracy
C. Long-term strategic alignment
D. Training evaluation
✅ Answer: A. Corrective actions are predefined for out-of-control conditions
Q66. Documentation of SOPs during control helps in:
A. Reducing process complexity
B. Sustaining standardization
C. Enhancing marketing reach
D. Increasing project duration
✅ Answer: B. Sustaining standardization
Q67. Which document marks the official closure of a Six Sigma project?
A. Charter
B. Closure Document
C. Pareto Report
D. VOC Summary
✅ Answer: B. Closure Document
Q68. Process ownership transfer is critical to ensure:
A. Financial reporting continues
B. Continuous accountability post-project
C. New project identification
D. Cost allocation
✅ Answer: B. Continuous accountability post-project
Q69. Which element of control focuses on “who does what, when, and how”?
A. Project Charter
B. SOPs
C. Measurement System Analysis
D. Fishbone Diagram
✅ Answer: B. SOPs
Q70. In SPC, points forming a consistent trend upward or downward indicate:
A. Random fluctuation
B. Assignable trend
C. Process centering
D. Statistical insignificance
✅ Answer: B. Assignable trend
Q71. The $\bar{X}$ and S chart is preferred when:
A. Sample size is small (n < 9)
B. Sample size is large (n ≥ 10)
C. Data are discrete
D. Process is attribute-based
✅ Answer: B. Sample size is large (n ≥ 10)
Q72. The “S” in $\bar{X}$ and S chart stands for:
A. Sampling interval
B. Standard deviation
C. Sample mean
D. Sigma level
✅ Answer: B. Standard deviation
Q73. The NP chart is designed for:
A. Defective proportions
B. Absolute number of defectives
C. Continuous measurements
D. Variable data
✅ Answer: B. Absolute number of defectives
Q74. Which chart is appropriate for varying sample sizes tracking defect proportion?
A. P Chart
B. C Chart
C. U Chart
D. XMR Chart
✅ Answer: A. P Chart
Q75. Control charts are considered effective only if:
A. Data are collected randomly and timely
B. Sample sizes are inconsistent
C. Control limits are omitted
D. SOPs are not followed
✅ Answer: A. Data are collected randomly and timely
Q76. Assignable causes in SPC refer to:
A. Random noise
B. Known, correctable sources of variation
C. Uncontrollable events
D. Customer dissatisfaction
✅ Answer: B. Known, correctable sources of variation
Q77. Common cause variation can be reduced by:
A. Routine control
B. Process redesign or improvement
C. Firefighting methods
D. Stopping production temporarily
✅ Answer: B. Process redesign or improvement
Q78. What does SPC stand for?
A. Statistical Performance Check
B. Statistical Process Control
C. Standardized Product Chart
D. Sample Probability Curve
✅ Answer: B. Statistical Process Control
Q79. SPC is primarily applied in which Six Sigma phase?
A. Define
B. Measure
C. Analyze
D. Control
✅ Answer: D. Control
Q80. The main difference between C Chart and U Chart is:
A. Sample size flexibility
B. Data type (variable vs. attribute)
C. Centerline calculation method
D. Number of operators
✅ Answer: A. Sample size flexibility
Q81. In control chart interpretation, “runs” refer to:
A. Defective units
B. Consecutive points on one side of the mean
C. Points outside limits
D. Batch variation
✅ Answer: B. Consecutive points on one side of the mean
Q82. In the Malgudi case, achieving process stability meant:
A. Random variation eliminated
B. Only natural variation remained
C. Output improved by chance
D. External causes ignored
✅ Answer: B. Only natural variation remained
Q83. Which of the following best ensures continuous compliance post-project?
A. Regular audits and reviews
B. One-time training
C. SPC elimination
D. Customer surveys
✅ Answer: A. Regular audits and reviews
Q84. The “width of the distribution” represents:
A. Process cost
B. Process variation
C. Team efficiency
D. Customer satisfaction
✅ Answer: B. Process variation
Q85. When the process average moves closer to the target, $C_{pk}$ will:
A. Decrease
B. Remain constant
C. Increase
D. Drop to zero
✅ Answer: C. Increase
Q86. In process capability studies, the “specification width” is given by:
A. USL + LSL
B. USL – LSL
C. (USL × LSL)/σ
D. (USL ÷ LSL) × Ïƒ
✅ Answer: B. USL – LSL
Q87. When a process is “not centered,” it implies:
A. Process mean is away from target
B. Standard deviation is zero
C. Mean equals median
D. Variation is nullified
✅ Answer: A. Process mean is away from target
Q88. Which parameter in Six Sigma reflects customer expectations numerically?
A. VOC
B. Specification limits
C. CTQ
D. Process map
✅ Answer: B. Specification limits
Q89. The number of defects expected per million opportunities is called:
A. COPQ
B. DPMO
C. CTQ
D. Z-value
✅ Answer: B. DPMO
Q90. In the Control phase, which metric ensures continuous data-driven validation?
A. Sigma level
B. Control chart
C. Pareto chart
D. Regression equation
✅ Answer: B. Control chart
Q91. In practical terms, the Control phase prevents:
A. Knowledge loss and performance backslide
B. Further improvement
C. Data reporting
D. Team reallocation
✅ Answer: A. Knowledge loss and performance backslide
Q92. The process capability index ($C_p$) is directly proportional to:
A. Process variation
B. Specification width
C. Defect rate
D. Time per unit
✅ Answer: B. Specification width
Q93. When USL = 120, LSL = 0, and σ = 10, what is $C_p$?
A. 2
B. 1
C. 3
D. 5
✅ Answer: A. 2
Q94. In a stable process, variation is said to be:
A. Predictable
B. Random and uncontrollable
C. Discontinuous
D. Infinite
✅ Answer: A. Predictable
Q95. What is the mathematical relationship between Z-value and sigma level?
A. They are inversely related
B. They are equivalent metrics
C. Z = 6 × sigma
D. Sigma = Z × DPMO
✅ Answer: B. They are equivalent metrics
Q96. Which Six Sigma phase ensures standardization of successful changes?
A. Analyze
B. Control
C. Define
D. Improve
✅ Answer: B. Control
Q97. Post-project financial benefits are typically monitored for:
A. 3 months
B. 6 months
C. 1 year
D. Indefinitely
✅ Answer: C. 1 year
Q98. Control plans help convert improvements into:
A. One-time events
B. Sustainable standard practices
C. Isolated experiments
D. Temporary gains
✅ Answer: B. Sustainable standard practices
Q99. Assignable causes must be eliminated to ensure:
A. Shorter cycle times
B. Process stability
C. Better marketing reach
D. Higher revenue
✅ Answer: B. Process stability
Q100. Continuous process improvement depends heavily on:
A. Regular control chart reviews
B. Decreasing data points
C. Increasing paperwork
D. Employee turnover
✅ Answer: A. Regular control chart reviews
Q101. In SPC interpretation, a single point beyond the upper control limit (UCL) signals:
A. Random noise
B. Out-of-control condition
C. Normal fluctuation
D. Natural variation
✅ Answer: B. Out-of-control condition
Q102. A Control Plan “handed over” to process owners signifies:
A. Completion of the Analyze phase
B. Transition to operational ownership
C. Beginning of the Improve phase
D. Data recalibration
✅ Answer: B. Transition to operational ownership
Q103. The ultimate aim of the Control phase is to:
A. Monitor financial metrics only
B. Maintain gains achieved from improvements
C. Return to the original process
D. Simplify DMAIC reporting
✅ Answer: B. Maintain gains achieved from improvements
Q104. Regular SPC-based auditing ensures:
A. Process remains predictable and stable
B. Employees are replaced
C. Sampling is reduced
D. Training costs decrease automatically
✅ Answer: A. Process remains predictable and stable
Q105. In Six Sigma language, the “voice of the process” is captured through:
A. VOC
B. Control Charts
C. CTQ
D. Benchmarking
✅ Answer: B. Control Charts
Q106. A process capability closer to 1.33 or higher indicates:
A. Excellent capability
B. Poor centering
C. High defect rate
D. Unstable performance
✅ Answer: A. Excellent capability
Q107. In project closure, documenting “lessons learned” mainly helps:
A. Reduce next project learning curve
B. Increase COPQ
C. Limit financial reviews
D. Reassign staff
✅ Answer: A. Reduce next project learning curve
Q108. Statistical Process Control supports which principle of Six Sigma?
A. Data-driven decision-making
B. Intuitive judgment
C. Cost-cutting without analysis
D. Random improvement
✅ Answer: A. Data-driven decision-making
Q109. A sustained Six Sigma improvement depends most on:
A. Leadership handover and control documentation
B. High control chart frequency
C. Cost optimization
D. Increased meetings
✅ Answer: A. Leadership handover and control documentation
Q110. The transition from Six Sigma project team to process owner represents:
A. Institutionalization of improvement
B. Start of new analysis
C. Temporary monitoring
D. Pilot run
✅ Answer: A. Institutionalization of improvement
Six Sigma Control Phase, SPC Tools, Process Capability, Control Plan, DMAIC, Cp Cpk, Process Stability, Statistical Process Control, Six Sigma MBA Practice, Lean Six Sigma Exam Prep
