Control Phase: SPC Flashcards
7 cards from real Lean Six Sigma Black Belt Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Control Phase: SPC flashcards as text
A multivariate control chart (e.g., Hotelling's T² chart) is preferred over separate univariate charts when:
Answer: Multiple correlated quality characteristics must be monitored simultaneously
Hotelling's T² chart monitors multiple correlated variables together, preventing inflated false alarm rates that occur when running many separate univariate charts.
The D4 constant on an R chart for a subgroup size of n=5 is approximately 2.114. This constant is used to calculate:
Answer: The upper control limit of the R chart
UCL_R = D4 × R-bar; for n=5, D4 ≈ 2.114, so the upper control limit is 2.114 times the average range.
Pre-control charts differ from standard SPC control charts primarily because they:
Answer: Use specification limits to set zones rather than calculated statistical control limits
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.
When transitioning a process from the Improve phase to Control, which action ensures the SPC chart remains relevant long-term?
Answer: Recalculating control limits based on the improved process baseline
After process improvement, new control limits must be calculated from the improved baseline to correctly reflect the new process capability and detect future deviations.
Zone C on a Western Electric control chart refers to the region between:
Answer: 0 and 1 sigma from the centerline
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.
A Six Sigma process has a process sigma level of 6, which corresponds to a defect rate of 3.4 DPMO. This calculation assumes:
Answer: A 1.5 sigma long-term process shift from the target
The 3.4 DPMO figure for a 6-sigma process incorporates the industry-standard assumption of a 1.5-sigma long-term shift in the process mean.
Which statement correctly describes the relationship between a process being 'in control' and 'capable'?
Answer: A process can be in control but not capable, capable but not in control, both, or neither
Statistical control (predictability) and capability (meeting specs) are independent: a process can be stable but centered outside specs, or meeting specs but erratically.