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
Which control chart is most appropriate for monitoring the number of defects per unit when the subgroup size varies?
Answer: u-chart
The u-chart monitors defects per unit and accommodates variable subgroup sizes, unlike the c-chart which requires a constant area of opportunity.
Process capability ratio Cp differs from Cpk in that Cp:
Answer: Ignores process centering while Cpk accounts for it
Cp measures only the spread relative to specifications without regard to centering, while Cpk adjusts for how far the process mean is from the nearest specification limit.
An EWMA chart uses a smoothing parameter λ (lambda). What happens when λ approaches 1?
Answer: The chart behaves more like a Shewhart individuals chart
As λ approaches 1, the EWMA chart places nearly all weight on the most recent observation, approximating a Shewhart individuals (I) chart.
Which situation would make a P-chart inappropriate?
Answer: When defects per unit are being tracked
The P-chart monitors the proportion of nonconforming items (pass/fail), not the count of defects per unit; for defects per unit, a u-chart or c-chart should be used.
In a Gage R&R study, which component of variation confirms that the measurement system discriminates between parts?
Answer: Part-to-part variation
Part-to-part variation being large relative to measurement system variation confirms the gage can distinguish between different parts, indicating adequate discrimination.
Which term describes a process that is in statistical control but produces output outside specification limits?
Answer: Stable but not capable
A process can be statistically stable (only common cause variation) yet still incapable if the natural process spread exceeds the specification width.
What is the effect of using 3-sigma control limits instead of 2-sigma limits on Type I error (false alarm rate)?
Answer: Decreases Type I error
Wider 3-sigma limits reduce the probability of falsely signaling a special cause when only common cause variation is present, thus decreasing the Type I error rate.