CRE Quality Control Procedures 3 — Questions and Answers
Question 1: In a double sampling plan, when is a second sample required?
- When the first sample result falls between the acceptance and rejection numbers (Correct answer)
- When the lot size exceeds 10,000 units
- When the AQL is set below 1.0%
- When the first sample contains zero defects
Correct answer: When the first sample result falls between the acceptance and rejection numbers
A second sample is drawn only when the first sample result is inconclusive — above the accept number but below the reject number.
Question 2: Which statistical measure best describes process spread in a capability study?
- Standard deviation (sigma) (Correct answer)
- Median
- Mode
- Range of the sample mean
Correct answer: Standard deviation (sigma)
Standard deviation quantifies the spread of individual measurements and is the basis for capability indices like Cp and Cpk.
Question 3: What is Average Outgoing Quality Limit (AOQL) in acceptance sampling?
- The maximum average defective rate in accepted lots after inspection and replacement (Correct answer)
- The maximum acceptable incoming defect rate before rejection
- The lowest achievable AQL for a given sample size
- The average defect rate of rejected lots returned to the supplier
Correct answer: The maximum average defective rate in accepted lots after inspection and replacement
AOQL is the worst-case average quality of lots that pass inspection, accounting for 100% inspection of rejected lots.
Question 4: A u-chart is used to monitor:
- The number of defects per unit when sample size varies (Correct answer)
- The proportion defective in equal-size samples
- The number of defective units in a fixed sample
- The individual measurements from a continuous process
Correct answer: The number of defects per unit when sample size varies
The u-chart tracks defects per unit and adjusts control limits for varying sample sizes, unlike the c-chart.
Question 5: Which approach to quality improvement focuses on reducing variation to achieve near-zero defects at 3.4 DPMO?
- Six Sigma (Correct answer)
- ISO 9001
- Total Quality Management
- Zero Defects program
Correct answer: Six Sigma
Six Sigma targets 3.4 defects per million opportunities, equating to 6 standard deviations between the process mean and the nearest specification limit.
Question 6: In a Shainin DOE approach, what is the 'Red X' concept?
- The dominant root cause variable responsible for most of the variation (Correct answer)
- The critical characteristic on an engineering drawing
- The highest-risk failure mode in an FMEA
- The first control chart limit exceeded
Correct answer: The dominant root cause variable responsible for most of the variation
Dorian Shainin's Red X identifies the single most dominant variable causing product variation or defects.
Question 7: What distinguishes a nonconformance from a defect in quality control terminology?
- A nonconformance is any failure to meet a specified requirement; a defect additionally implies fitness-for-use failure or safety concern (Correct answer)
- A defect is a minor issue while a nonconformance is a major issue
- Nonconformances apply only to documents while defects apply to products
- They are interchangeable terms with no practical distinction
Correct answer: A nonconformance is any failure to meet a specified requirement; a defect additionally implies fitness-for-use failure or safety concern
Nonconformance refers to any deviation from specifications, while 'defect' carries legal implications regarding fitness for use.
CRE Quality Control Procedures 3
In a double sampling plan, when is a second sample required?