Lean Six Sigma Green Belt Certification Control Phase and Sustainment 2 — Questions and Answers
Question 1: A Green Belt notices a control chart with a run of 8 consecutive points above the centerline. What action should be taken?
- Continue monitoring since no points are outside control limits
- Investigate for a special cause even though limits are not breached (Correct answer)
- Recalculate control limits using only the recent data
- Declare the process out of control and shut it down
Correct answer: Investigate for a special cause even though limits are not breached
Eight consecutive points on one side of the centerline is a non-random pattern (Western Electric Rule) indicating a special cause that requires investigation regardless of control limit violations.
Question 2: Which document is MOST effective for ensuring operators consistently follow a newly optimized process?
- Project charter
- SIPOC diagram
- Standard Operating Procedure (SOP) (Correct answer)
- Fishbone diagram
Correct answer: Standard Operating Procedure (SOP)
A Standard Operating Procedure (SOP) provides step-by-step instructions that standardize how operators perform tasks, directly supporting process sustainment.
Question 3: During a control plan review, the team finds that a CTQ characteristic has a Cpk of 0.85. What does this indicate?
- The process is highly capable and no action is needed
- The process is centered but slightly variable
- The process is not capable and is producing defects (Correct answer)
- The process is capable only when centered exactly
Correct answer: The process is not capable and is producing defects
A Cpk below 1.0 indicates the process is not capable of consistently meeting specifications and is likely producing defects or out-of-spec output.
Question 4: What is the PRIMARY purpose of a response plan within a control plan?
- To document the measurement system used for each CTQ
- To describe corrective actions when a process goes out of control (Correct answer)
- To list all process inputs and their target values
- To assign ownership of the control chart to a specific person
Correct answer: To describe corrective actions when a process goes out of control
A response plan specifies the corrective actions operators and supervisors should take when a control chart signals an out-of-control condition.
Question 5: A team implementing statistical process control (SPC) should establish control limits using data from:
- The desired specification limits provided by the customer
- A period when the process was known to be stable and in control (Correct answer)
- The worst-case scenarios observed during the Measure phase
- Theoretical normal distribution parameters
Correct answer: A period when the process was known to be stable and in control
Control limits must be calculated from historical data collected when the process was stable, so they reflect natural process variation rather than specification requirements.
Question 6: Which type of control chart is BEST suited for monitoring the proportion of defective items in a process with varying subgroup sizes?
- X-bar and R chart
- np chart
- p chart (Correct answer)
- c chart
Correct answer: p chart
The p chart monitors the proportion of defectives and automatically adjusts control limits for varying subgroup sizes, making it appropriate when sample sizes differ.
Question 7: Visual management tools in a control system serve to:
- Replace the need for statistical control charts entirely
- Make process status immediately apparent to anyone on the floor (Correct answer)
- Reduce the number of measurements needed in the control plan
- Transfer responsibility from operators to management
Correct answer: Make process status immediately apparent to anyone on the floor
Visual management (e.g., color-coded gauges, shadow boards, andon lights) makes the current process state instantly visible so that abnormalities are noticed quickly by everyone.
Lean Six Sigma Green Belt Certification Control Phase and Sustainment 2
A Green Belt notices a control chart with a run of 8 consecutive points above the centerline.
What action should be taken?