Quality Auditor Certification Statistical Sampling 5 β Questions and Answers
Question 1: In a variables sampling plan using the k-method, acceptance occurs when the quality statistic k satisfies which condition?
- k is less than the acceptance constant k_a
- k is greater than or equal to the acceptance constant k_a (Correct answer)
- k equals exactly the AQL value
- k exceeds the sample standard deviation
Correct answer: k is greater than or equal to the acceptance constant k_a
In the k-method, the quality statistic k = (XΜ - L)/s (or similar) must meet or exceed k_a to indicate the process is sufficiently far from the specification limit.
Question 2: What is the primary reason acceptance sampling does NOT improve quality?
- It uses too small a sample to detect defects
- It only sorts defective product from conforming product rather than preventing defects (Correct answer)
- It requires 100% inspection to be effective
- It cannot detect attribute defects
Correct answer: It only sorts defective product from conforming product rather than preventing defects
Acceptance sampling is a screening tool, not a prevention tool; defects must already exist in the lot for sampling to detect them.
Question 3: A quality auditor selects General Inspection Level II in ANSI/ASQ Z1.4. Compared to Level I, Level II provides:
- Smaller sample sizes with greater discrimination
- Larger sample sizes with better discrimination between good and bad lots (Correct answer)
- Equal sample sizes but stricter acceptance numbers
- Reduced inspection regardless of quality history
Correct answer: Larger sample sizes with better discrimination between good and bad lots
Level II uses larger samples than Level I, providing a steeper OC curve and better ability to discriminate between acceptable and rejectable lots.
Question 4: In sequential probability ratio testing (SPRT), inspection continues until:
- A fixed sample size is reached
- Cumulative evidence reaches an accept or reject boundary (Correct answer)
- The defect count exceeds the AQL
- The inspector completes the shift
Correct answer: Cumulative evidence reaches an accept or reject boundary
SPRT compares cumulative likelihood ratios against accept/reject boundaries, stopping as soon as sufficient evidence accumulates.
Question 5: When the incoming lot quality is very good (near zero defects), the AOQ value is approximately:
- Equal to the AOQL
- Near zero, because most lots are accepted and contain very few defects (Correct answer)
- Equal to the AQL
- At its maximum because few lots are rejected and screened
Correct answer: Near zero, because most lots are accepted and contain very few defects
When incoming quality is near zero, outgoing quality is also near zero because the few accepted lots contain almost no defectives.
Question 6: A quality auditor calculates a 95% confidence interval for a defect proportion as [0.03, 0.09]. The correct interpretation is:
- There is a 95% probability the true proportion is between 3% and 9%
- If this procedure were repeated many times, 95% of such intervals would contain the true proportion (Correct answer)
- The process is acceptable because the interval does not include zero
- The sample size was too small to be meaningful
Correct answer: If this procedure were repeated many times, 95% of such intervals would contain the true proportion
Frequentist confidence intervals mean that 95% of identically constructed intervals would capture the true parameter; the specific interval either does or doesn't.
Question 7: In acceptance sampling, switching from a single sampling plan to a double sampling plan with the same AQL and LTPD protection will typically:
- Increase the average sample number inspected per lot
- Reduce the average sample number but require more administrative complexity (Correct answer)
- Provide less protection against bad lots at equal sample sizes
- Require 100% inspection of every second lot
Correct answer: Reduce the average sample number but require more administrative complexity
Double sampling reduces the average sample number (ASN) compared to single sampling because many lots are decided on the first sample, but it adds complexity.
Quality Auditor Certification Statistical Sampling 5
In a variables sampling plan using the k-method, acceptance occurs when the quality statistic k satisfies which condition?