Lean Six Sigma Yellow Belt Certification Control and Sustainment Methods 2 — Questions and Answers
Question 1: On a control chart, what does it mean when a single data point falls beyond the Upper Control Limit (UCL)?
- The process is in statistical control
- A special cause of variation is likely present (Correct answer)
- The specification limit has been exceeded
- The sample size should be reduced
Correct answer: A special cause of variation is likely present
A point beyond the UCL is one of the Western Electric rules indicating a special cause of variation that requires investigation.
Question 2: A control plan should be updated whenever:
- A new employee joins the team
- A process change or improvement is implemented (Correct answer)
- Monthly audits are completed
- The project budget is revised
Correct answer: A process change or improvement is implemented
Control plans must reflect the current process state, so any process change or improvement requires an update to keep the plan accurate.
Question 3: Which type of control chart is best suited for monitoring the proportion of defective items in a process?
- X-bar and R chart
- I-MR chart
- p-chart (Correct answer)
- c-chart
Correct answer: p-chart
A p-chart tracks the proportion (fraction) of nonconforming items and is used when sample sizes may vary.
Question 4: What is the primary purpose of a response plan within a control plan?
- To define who owns the process
- To outline corrective actions when a process goes out of control (Correct answer)
- To document the history of improvements
- To set the measurement frequency
Correct answer: To outline corrective actions when a process goes out of control
A response plan tells operators exactly what steps to take when control chart signals indicate the process is out of control.
Question 5: In a control chart, the Lower Control Limit (LCL) is calculated as:
- Mean minus 2 standard deviations
- Mean minus 3 standard deviations (Correct answer)
- The lower specification limit
- The minimum observed value
Correct answer: Mean minus 3 standard deviations
Control limits are set at ±3 standard deviations from the process mean, so the LCL = mean − 3σ.
Question 6: Which of the following is a benefit of using Statistical Process Control (SPC) in the Control phase?
- It eliminates all process variation
- It detects shifts in process performance before defects are produced in large quantities (Correct answer)
- It removes the need for control plans
- It replaces the need for operator training
Correct answer: It detects shifts in process performance before defects are produced in large quantities
SPC enables early detection of process drift or shifts so corrective action can be taken before many defects occur.
Question 7: What does 'common cause variation' on a control chart indicate?
- An equipment failure has occurred
- The process is behaving normally and is in statistical control (Correct answer)
- A special event disrupted the process
- The operator made an error
Correct answer: The process is behaving normally and is in statistical control
Common cause variation is the natural, inherent variability of a stable process and does not require special investigation.
