Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt Control Phase and Sustainment 1

Question 1

In the Control phase, what is the primary function of a control chart's Upper Control Limit (UCL)?

Accepted Answer

To signal when a process has shifted beyond natural variation

Answer

The UCL (and LCL) on a control chart represent the boundaries of natural process variation (±3 sigma). A data point beyond the UCL signals a special-cause event requiring investigation, not just common-cause noise.

Question 2

Which of the following best describes a 'mistake-proofing' device implemented during the Control phase?

Accepted Answer

A physical or electronic mechanism that prevents a defect from occurring or escaping

Answer

Poka-yoke (mistake-proofing) devices are physical or automated mechanisms — like sensors, jigs, or interlocks — that either prevent an error from happening or detect it immediately. They are more robust than procedural controls like checklists.

Question 3

A Lean Six Sigma team has completed improvements and is closing the project. Which metric best indicates that gains have been sustained six months after handover?

Accepted Answer

The process sigma level remaining at or above the improved baseline

Answer

Sustained improvement is demonstrated by ongoing process performance data — specifically, the sigma level (or defect rate) remaining at or above the level achieved during the Improve phase, confirming the gains have held.

Question 4

What is the purpose of a 'lessons learned' document completed at the end of the Control phase?

Accepted Answer

To capture knowledge and best practices so future projects can benefit from the team's experience

Answer

A lessons learned document captures insights — what worked, what didn't, and what would be done differently — enabling organizational learning and preventing future teams from repeating the same mistakes.

Question 5

When selecting a control chart type in the Control phase, which chart is appropriate for monitoring the proportion of defective units in a variable-size subgroup?

Accepted Answer

p-chart

Answer

The p-chart monitors the proportion (fraction) defective and is designed for attribute data where subgroup sizes vary. The c-chart tracks count of defects per unit in fixed-size subgroups, while X-bar/R and I-MR charts are for continuous data.

Lean Six Sigma Green Belt Certification Practice Test

Lean Six Sigma Green Belt Certification Practice Test

Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt Control Phase and Sustainment 1