Process Capability Analysis Flashcards
7 cards from real Certified Six Sigma Black Belt Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Process Capability Analysis flashcards as text
The standard '1.5 sigma shift' used in Six Sigma calculations accounts for which source of variation?
Answer: Typical long-term drift of the process mean over time
The 1.5 sigma shift reflects the empirical observation that process means typically drift by up to 1.5σ over long periods due to factors like tool wear, material changes, and environmental shifts.
What is the recommended minimum sample size for a reliable process capability study?
Answer: Approximately 100 data points (or 30+ subgroups of 3–5)
Industry guidelines recommend approximately 100 data points — or at least 30 subgroups of 3 to 5 samples — to obtain statistically stable and reliable capability index estimates.
If a process has Cp = 2.0 and is perfectly centered, what sigma level does this represent?
Answer: 6 sigma
Using Z = 3 × Cp, a Cp of 2.0 gives Z = 6, meaning the specification limits are 6 standard deviations from the perfectly centered process mean.
In Six Sigma terminology, 'first pass yield' (FPY) is best defined as:
Answer: Percentage of units completing a process step without any defect the first time
First Pass Yield (FPY) measures the percentage of units that pass through a process step correctly the first time, without requiring rework, repair, or scrap.
What is the fundamental difference between a control limit and a specification limit?
Answer: Control limits are statistically derived from process data; specification limits are set by customer or engineering requirements
Control limits (±3σ) come from the Voice of the Process and reflect natural variation, while specification limits come from the Voice of the Customer and define acceptable output.
A Black Belt finds Cp = 1.8 and Cpk = 0.6 for a critical process. What is the highest-priority corrective action?
Answer: Center the process mean within the specification limits
Cp = 1.8 confirms adequate process spread, but Cpk = 0.6 reveals severe off-centering; correcting the process mean position will immediately improve Cpk without changing the natural variation.
Which approach is valid for performing capability analysis when process data follows an exponential distribution?
Answer: Transform the data (e.g., Box-Cox) to achieve normality, or use non-normal distribution-fitting methods
For exponential or other non-normal distributions, both data transformation (to satisfy normality assumptions) and fitting the actual non-normal distribution are statistically valid approaches.