Statistical Process Control (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 Statistical Process Control (SPC) flashcards as text
A Black Belt observes that the R-chart shows statistical control, but the X-bar chart shows several out-of-control points. What is the correct interpretation?
Answer: The process mean has shifted while variability remains stable
An in-control R-chart with out-of-control X-bar points indicates that process spread is stable but the process mean has shifted, a classic sign of a location-type special cause.
Which of the following best describes 'rational subgrouping'?
Answer: Forming subgroups so within-subgroup variation represents only common cause variation
Rational subgrouping means forming subgroups so that variation within each subgroup reflects only natural, common cause variation, making between-subgroup shifts detectable.
What sigma level corresponds to a defect rate of approximately 3.4 DPMO in the Motorola/Six Sigma convention?
Answer: 6 sigma
In the Six Sigma convention, a 6-sigma process yields 3.4 DPMO, accounting for the standard 1.5-sigma long-term mean shift assumption.
A Levey-Jennings chart is most commonly used in which industry application of SPC?
Answer: Clinical laboratory quality control
Levey-Jennings charts are a standard SPC tool in clinical laboratories for monitoring analytical quality control materials and detecting assay drift.
When a process exhibits autocorrelation, using standard Shewhart control charts will most likely result in:
Answer: Control limits that are too narrow, causing excessive false alarms
Positive autocorrelation reduces the estimated within-subgroup variability, leading to artificially narrow control limits and inflated false alarm rates on Shewhart charts.
Which statistic is plotted on a median chart (X-tilde chart) instead of the subgroup average?
Answer: The middle value of the ranked subgroup observations
The median chart plots the middle (median) value of each subgroup, offering a simpler calculation that is also robust to outliers compared to the mean.
In Phase I SPC analysis, what is the primary objective?
Answer: Establish baseline control limits from historical data after removing assignable causes
Phase I SPC involves retrospective analysis of historical data to identify and remove special causes, establishing stable baseline control limits for future monitoring (Phase II).