Lean Six Sigma Black Belt Certification Control Phase: SPC 5

Question 1

A multivariate control chart (e.g., Hotelling's T² chart) is preferred over separate univariate charts when:

Accepted Answer

Multiple correlated quality characteristics must be monitored simultaneously

Answer

Hotelling's T² chart monitors multiple correlated variables together, preventing inflated false alarm rates that occur when running many separate univariate charts.

Question 2

The D4 constant on an R chart for a subgroup size of n=5 is approximately 2.114. This constant is used to calculate:

Accepted Answer

The upper control limit of the R chart

Answer

UCL_R = D4 × R-bar; for n=5, D4 ≈ 2.114, so the upper control limit is 2.114 times the average range.

Question 3

Pre-control charts differ from standard SPC control charts primarily because they:

Accepted Answer

Use specification limits to set zones rather than calculated statistical control limits

Answer

Pre-control uses zones defined by the specification limits (green = middle half of spec, yellow = outer quarters, red = beyond spec) rather than statistically derived control limits.

Question 4

When transitioning a process from the Improve phase to Control, which action ensures the SPC chart remains relevant long-term?

Accepted Answer

Recalculating control limits based on the improved process baseline

Answer

After process improvement, new control limits must be calculated from the improved baseline to correctly reflect the new process capability and detect future deviations.

Question 5

Zone C on a Western Electric control chart refers to the region between:

Accepted Answer

0 and 1 sigma from the centerline

Answer

Zone C is the innermost zone spanning 0 to 1 sigma on each side of the centerline; Zone B is 1–2 sigma, and Zone A is 2–3 sigma.

Lean Six Sigma Black Belt Certification Practice Test

Lean Six Sigma Black Belt Certification Practice Test

Lean Six Sigma Black Belt Certification Control Phase: SPC 5